I have been using OpenTK with mono on Fedora and have not seen that error. Your example uses some C# features I'm not familiar with, and I don't know what is in your draw sphere, so I have created a simple example that works on Linux below. Although only a triangle is drawn, it uses the shaders, and I enabled and disabled the shader programs as you have in your example above.

I assume you already have a GLControl you can pass into this function. My program sets up a 512 x 512 GLControl like this before calling the test function:

    static string VertexShader = 
    "float;" +
    "attribute vec4 vPosition;" +
    "void main()" +
    "{" +
        "gl_Position = vPosition;" +
    "}";    

    static string FragmentShader = 
    "float;" +
    "uniform vec4 vColor;" +
    "void main()" +
    
    "{" +
        "gl_FragColor = vColor * 1.0 / 256.0 + 1.0 / 256.0 * vec4(gl_FragCoord.x, gl_FragCoord.y, gl_FragCoord.z, 1);" + // (1-clamp(gl_FragCoord.z - 0.05, 0, 1));" +
    "}";        
                    
    static int programId;
    
    static OpenTK.GLControl GlControl;
    
    static bool setup_complete = false;
    
    public static StringBuilder Test(OpenTK.GLControl GlControl_in)
    {
        StringBuilder result = new StringBuilder();
        if (setup_complete == false)
        {               
            GlControl = GlControl_in;
            Compile();
            result.AppendLine("Compile Complete");
            setup_complete = true;              
        }
        
        Apply();
        result.AppendLine("Apply Complete");
        DrawSomething();
        Unapply();
        result.AppendLine("UnApply Complete");
        Apply();
        result.AppendLine("Apply Complete");
        DrawSomething();
        Unapply();
        result.AppendLine("UnApply Complete");
        return result;
    }
    
    public static int loadShader(ShaderType type, String shaderCode)
    {
        int shader_ok;
        // create a vertex shader type (GLES20.GL_VERTEX_SHADER)
        // or a fragment shader type (GLES20.GL_FRAGMENT_SHADER)
        int shader = GL.CreateShader(type);

        // add the source code to the shader and compile it
        GL.ShaderSource(shader, shaderCode);
        GL.CompileShader(shader);
        GL.GetShader(shader, ShaderParameter.CompileStatus, out shader_ok);
        if (shader_ok == 0) {
            MessageBox.Show("Failed to compile " + shaderCode);
            //fprintf(stderr, "Failed to compile %s:\n", filename);
            //show_info_log(shader, glGetShaderiv, glGetShaderInfoLog);
            //glDeleteShader(shader);
            return 0;
        }

        return shader;
    }
    
    public static void Compile()
    {   
        int VshaderId = loadShader(ShaderType.VertexShader, VertexShader);
        int FshaderId = loadShader(ShaderType.FragmentShader, FragmentShader);
        programId = GL.CreateProgram();
        GL.AttachShader(programId, VshaderId);
        GL.AttachShader(programId, FshaderId);
        GL.LinkProgram(programId);
        int program_ok;
        GL.GetProgram(programId, ProgramParameter.LinkStatus, out program_ok);
        if (program_ok == 0)
        {
            MessageBox.Show("Failed to link " + program_ok.ToString());
        }
    }
    
    public static void Apply()
    {
        if (programId == -1)
            throw new InvalidOperationException("Compile() has to be called before Apply()");
        GL.UseProgram(programId);
    }
    
    public static void Unapply()
    {
        GL.UseProgram(0);
    }
    
    static int mColorHandle;
    
    // Set color with red, green, blue and alpha (opacity) values
    static OpenTK.Graphics.Color4 color = new OpenTK.Graphics.Color4(0.5f, 0.5f, 0.5f, 1.0f);

    private static void DrawTriangle()
    {
        //GL.MatrixMode(MatrixMode.Modelview);
        //GL.LoadIdentity();
        GL.Color3(Color.Yellow);
        GL.Begin(BeginMode.Triangles);
        GL.Vertex3(0.0, 1, -1);
        GL.Vertex3(-1, -1, 0);
        GL.Vertex3(1, -1, 1);
        GL.End();
    }

    public static void DrawSomething()
    {           
        GL.Clear(ClearBufferMask.ColorBufferBit | ClearBufferMask.DepthBufferBit);

        // get handle to fragment shader's vColor member
        mColorHandle = GL.GetUniformLocation(programId, "vColor");

        // Set color for drawing the triangle
        GL.Uniform4(mColorHandle, color);
                    
        DrawTriangle();
        
        GlControl.SwapBuffers();
    }
}

}

Hope that helps.

James

I have been using OpenTK with mono on Fedora and have not seen that error. Your example uses some C# features I'm not familiar with, and I don't know what is in your draw sphere, so I have created a simple example that works on Linux below.

Although only a triangle is drawn, it uses the shaders, and I enabled and disabled the shader programs as you have in your example above.

I assume you already have a GLControl you can pass into this function. My program sets up a 512 x 512 GLControl like this before calling the test function:

int w = GlControl1.Width;
int h = GlControl1.Height;
GL.MatrixMode (MatrixMode.Projection);
GL.LoadIdentity ();
GL.Ortho (0, w, 0, h, -1, 1); // Bottom-left corner pixel has coordinate (0, 0)
GL.Viewport (0, 0, w, h); // Use all of the glControl painting area



using System;
using System.Text;
using System.Drawing;
using OpenTK;
using OpenTK.Graphics.OpenGL;
using System.Windows.Forms;

namespace OpenTkTestNamespace
{
    public class StackExchangeTestsClass
    {
        public StackExchangeTestsClass()
        {
        }
        
        static string VertexShader = 
        "float;" +
        "attribute vec4 vPosition;" +
        "void main()" +
        "{" +
            "gl_Position = vPosition;" +
        "}";    

        static string FragmentShader = 
        "float;" +
        "uniform vec4 vColor;" +
        "void main()" +
        
        "{" +
            "gl_FragColor = vColor * 1.0 / 256.0 + 1.0 / 256.0 * vec4(gl_FragCoord.x, gl_FragCoord.y, gl_FragCoord.z, 1);" + // (1-clamp(gl_FragCoord.z - 0.05, 0, 1));" +
        "}";        
                        
        static int programId;
        
        static OpenTK.GLControl GlControl;
        
        static bool setup_complete = false;
        
        public static StringBuilder Test(OpenTK.GLControl GlControl_in)
        {
            StringBuilder result = new StringBuilder();
            if (setup_complete == false)
            {               
                GlControl = GlControl_in;
                Compile();
                result.AppendLine("Compile Complete");
                setup_complete = true;              
            }
            
            Apply();
            result.AppendLine("Apply Complete");
            DrawSomething();
            Unapply();
            result.AppendLine("UnApply Complete");
            Apply();
            result.AppendLine("Apply Complete");
            DrawSomething();
            Unapply();
            result.AppendLine("UnApply Complete");
            return result;
        }
        
        public static int loadShader(ShaderType type, String shaderCode)
        {
            int shader_ok;
            // create a vertex shader type (GLES20.GL_VERTEX_SHADER)
            // or a fragment shader type (GLES20.GL_FRAGMENT_SHADER)
            int shader = GL.CreateShader(type);

            // add the source code to the shader and compile it
            GL.ShaderSource(shader, shaderCode);
            GL.CompileShader(shader);
            GL.GetShader(shader, ShaderParameter.CompileStatus, out shader_ok);
            if (shader_ok == 0) {
                MessageBox.Show("Failed to compile " + shaderCode);
                //fprintf(stderr, "Failed to compile %s:\n", filename);
                //show_info_log(shader, glGetShaderiv, glGetShaderInfoLog);
                //glDeleteShader(shader);
                return 0;
            }

            return shader;
        }
        
        public static void Compile()
        {   
            int VshaderId = loadShader(ShaderType.VertexShader, VertexShader);
            int FshaderId = loadShader(ShaderType.FragmentShader, FragmentShader);
            programId = GL.CreateProgram();
            GL.AttachShader(programId, VshaderId);
            GL.AttachShader(programId, FshaderId);
            GL.LinkProgram(programId);
            int program_ok;
            GL.GetProgram(programId, ProgramParameter.LinkStatus, out program_ok);
            if (program_ok == 0)
            {
                MessageBox.Show("Failed to link " + program_ok.ToString());
            }
        }
        
        public static void Apply()
        {
            if (programId == -1)
                throw new InvalidOperationException("Compile() has to be called before Apply()");
            GL.UseProgram(programId);
        }
        
        public static void Unapply()
        {
            GL.UseProgram(0);
        }
        
        static int mColorHandle;
        
        // Set color with red, green, blue and alpha (opacity) values
        static OpenTK.Graphics.Color4 color = new OpenTK.Graphics.Color4(0.5f, 0.5f, 0.5f, 1.0f);
    
        private static void DrawTriangle()
        {
            //GL.MatrixMode(MatrixMode.Modelview);
            //GL.LoadIdentity();
            GL.Color3(Color.Yellow);
            GL.Begin(BeginMode.Triangles);
            GL.Vertex3(0.0, 1, -1);
            GL.Vertex3(-1, -1, 0);
            GL.Vertex3(1, -1, 1);
            GL.End();
        }
    
        public static void DrawSomething()
        {           
            GL.Clear(ClearBufferMask.ColorBufferBit | ClearBufferMask.DepthBufferBit);

            // get handle to fragment shader's vColor member
            mColorHandle = GL.GetUniformLocation(programId, "vColor");

            // Set color for drawing the triangle
            GL.Uniform4(mColorHandle, color);
                        
            DrawTriangle();
            
            GlControl.SwapBuffers();
        }
    }
}

Hope that helps.