getting data from mysql database by using thread in vb.,net

I'm trying to get data from database but I got an error:

There is already an open DataReader associated with this Connection which must be closed first

what I did is the following codes:

1: I have a module that contains the following sub:

Public Function CheckServerConn() As Boolean
        Try
            _ServerConnStr = New MySqlConnection(My.Settings.DbPath)
            If _ServerConnStr.State = ConnectionState.Open Then
                _ServerConnStr.Close()
            End If

            If _ServerConnStr.State = ConnectionState.Closed Then
                _ServerConnStr.Open()
                Return True
            End If

        Catch ex As Exception
            MsgBox("Check The Conn " & ex.Message, Me_MsgInfoStyle, Me_MsgCaptionStr)
            Return False
        End Try
#Disable Warning BC42353 ' Function doesn't return a value on all code paths
    End Function

2: I have this subroutine in class called "ClsMySql":

'GetData
    Public Sub GetData(ByVal SqlStr As String, ByVal xDt As DataTable, ByVal xPar() As MySqlParameter)
        Using xCmd As New MySqlCommand() With {
                    .CommandType = CommandType.Text,
                    .CommandText = SqlStr,
                    .Connection = _ServerConnStr,
                    .CommandTimeout = 5000000
                    }

            If xPar IsNot Nothing Then
                For i As Integer = 0 To xPar.Length - 1
                    xCmd.Parameters.Add(xPar(i))
                Next
            End If

            Using xDa As New MySqlDataAdapter(xCmd)
                xDa.Fill(xDt)
            End Using
            xDt.Dispose()
        End Using
    End Sub

3: I have a class for the table that have the following method:

Public Sub MySql_Get_Daf()
    xClsMySql = New ClsMySql
    Dim SqlStr As String = "SELECT RegID,RegType, tblregs1.`RegRef`,`RegDate`, COUNT(`RegdID`) AS xCount 
                        ,IF(COUNT(`RegdID`) =3,'Ok','Error') AS xResult FROM tblregs1
                        INNER JOIN tblregs2 ON tblregs2.RegRef = tblregs1.RegRef
                        WHERE `RegType` = 'Daf'
                        GROUP BY tblregs1.`RegRef`  
                        ORDER BY COUNT(`RegdID`)  ASC"
    Dt_Get_Daf = New DataTable()
    xClsMySql.GetData(SqlStr, Dt_Get_Daf, Nothing)

End Sub

Public Sub MySql_Get_Qbd()
    xClsMySql = New ClsMySql
    Dim SqlStr As String = "SELECT RegID,RegType, tblregs1.`RegRef`,`RegDate`, COUNT(`RegdID`) AS xCount 
                        ,IF(COUNT(`RegdID`) =3,'Ok','Error') AS xResult FROM tblregs1
                        INNER JOIN tblregs2 ON tblregs2.RegRef = tblregs1.RegRef
                        WHERE `RegType` = 'Qbd'
                        GROUP BY tblregs1.`RegRef`  
                        ORDER BY COUNT(`RegdID`)  ASC"
    Dt_Get_Qbd = New DataTable()
    xClsMySql.GetData(SqlStr, Dt_Get_Qbd, Nothing)
End Sub

Public Sub MySql_Get_All()
    Dim xThread As Thread = New Thread(Sub() MySql_Get_Daf())
    Dim xThread2 As Thread = New Thread(Sub() MySql_Get_Qbd())

    xThread.Start()
    xThread2.Start()

End Sub

when I call MySql_Get_All by a button it gives me the next error:

There is already an open DataReader associated with this Connection which must be closed first

can anybody tell me what's the wrong here