"System.Data.OleDb.OleDbException: 'Syntax error in INSERT INTO statement.'" [duplicate]

I've got an error message:

System.Data.OleDb.OleDbException: 'Syntax error in INSERT INTO statement.'

I've read through multiple questions like this, but non of their answers helped me.

This is my code:

conn.Open();

string sql = "";
sql = "insert into player(Username, Password) values(@Username, @Password)";

using (command = new OleDbCommand(sql, conn))
{
    command.Parameters.AddWithValue("@Username", textBoxUsername.Text);
    command.Parameters.AddWithValue("@Password", textBoxPassword.Text);
    command.ExecuteNonQuery();
}
command.Dispose();
conn.Close();

The error is in the following line:

command.ExecuteNonQuery();

Does anyone know a solution for this error?

Thanks in advance!