Why does this code always get a SynchronizationLockException?

What is wrong with this code?

I always get

The object synchronization method was called from an unsynchronized code block

An exception

System.Threading.Monitor.Exit(m_sqlConnection)

But ... It doesn’t matter if I put the Monitor statement inside or outside the try-catch-finally-block in any combination, I always get this exception.

That is, after I compiled the code. If I let it run again after receiving the first exception, it works fine ... It's always after recompiling ...

Public Shared Function GetDataTable(ByRef strSQL As String, ByRef dt As System.Data.DataTable, Optional ByRef strTableName As String = "ThisTable") As Integer
            Dim daQueryTable As System.Data.SqlClient.SqlDataAdapter = Nothing



            Try
                System.Threading.Monitor.TryEnter(m_sqlConnection, 5000)

                If isDataBaseConnectionOpen() = False Then OpenSQLConnection()


                daQueryTable = New System.Data.SqlClient.SqlDataAdapter(strSQL, m_sqlConnection)
                dt = New System.Data.DataTable(strTableName)

                daQueryTable.Fill(dt)
            Catch ex As Exception
                Log(ex)
                Return -1
            Finally
                m_sqlConnection.Close()
                System.Threading.Monitor.Exit(m_sqlConnection)
                daQueryTable.Dispose()
                daQueryTable = Nothing
            End Try

            Return dt.Rows.Count
        End Function ' GetDataTable

C # Version:

public static int GetDataTable(ref string strSQL, ref System.Data.DataTable dt, ref string strTableName = "ThisTable")
{
    System.Data.SqlClient.SqlDataAdapter daQueryTable = null;



    try {
        System.Threading.Monitor.TryEnter(m_sqlConnection, 5000);

        if (isDataBaseConnectionOpen() == false)
            OpenSQLConnection();


        daQueryTable = new System.Data.SqlClient.SqlDataAdapter(strSQL, m_sqlConnection);
        dt = new System.Data.DataTable(strTableName);

        daQueryTable.Fill(dt);
    } catch (Exception ex) {
        Log(ex);
        return -1;
    } finally {
        m_sqlConnection.Close();
        System.Threading.Monitor.Exit(m_sqlConnection);
        daQueryTable.Dispose();
        daQueryTable = null;
    }

    return dt.Rows.Count;
} // GetDataTable