FieldMapping Not Valid For Matching Mappings..

Sub SyncDatabases(ByVal sServerName As String)
        '
        ' Redgate Declarations
        '
        Dim dSourceDatabase As New RedGate.SQLCompare.Engine.Database
        Dim dTargetDatabase As New RedGate.SQLCompare.Engine.Database
        Dim oTBLMap As New RedGate.SQLDataCompare.Engine.TableMappings
        Dim oTBLMapping As RedGate.SQLDataCompare.Engine.TableMapping
        Dim oRedGateSession As New RedGate.SQLDataCompare.Engine.ComparisonSession
        '
        ' VB.Net SQL Declarations
        '
        Dim oProvider As New SqlProvider
        Dim myConnString As String = "User Id=lvadmin;Password=lvadmin;Initial Catalog=Labelsync;Server=" & sServerName
        Dim mySelectQuery As String = "SELECT SourceDB,TargetDB,TBLToCompare,Fields,ComparisonType FROM Tables_To_Compare Where (Active=1) Order By ComparisonOrder"
        Dim myConnection As New System.Data.SqlClient.SqlConnection(myConnString)
        Dim myCommand As New System.Data.SqlClient.SqlCommand(mySelectQuery, myConnection)
        Dim myReader As System.Data.SqlClient.SqlDataReader
        '
        ' Misc Declarations
        '
        Dim I As Integer
        Dim aFields As String()
        '
        ' Connection and statements To Setup DBReader
        '
        ' We will read a table that has the following fields
        '
        ' SourceDB - The 'master' database
        ' TargetDB - The 'Target' database
        ' tblToCompare - The Database Table To Compare
        ' Fields - Fields To Map, Comma Delimited  IE:  Top Level Assy Number, Plant Code, MFG_ID1
        ' ComparisonType - VT,TT
        '
        Try
            myConnection.Open()
            myReader = myCommand.ExecuteReader()
            While myReader.Read
                '
                ' All Databases will use lvadmin for userid and password
                '
                dSourceDatabase.RegisterForDataCompare(New ConnectionProperties(sServerName, myReader("SourceDB").ToString, "lvadmin", "lvadmin"))
                dTargetDatabase.RegisterForDataCompare(New ConnectionProperties(sServerName, myReader("TargetDB").ToString, "lvadmin", "lvadmin"))
                '
                ' Setup Our Mappings
                '
                ' VT Means Compare a VIEW to a TABLE
                ' TT Means Compare a TABLE to a TABLE
                '
                Select Case myReader("ComparisonType").ToString.Trim.ToUpper
                    Case "VT" : oTBLMapping = oTBLMap.Join(dSourceDatabase.Views("[dbo].[" + myReader("tblToCompare").ToString.Trim + "]"), dTargetDatabase.Tables("[dbo].[" + myReader("tblToCompare").ToString.Trim + "]"))
                    Case "TT" : oTBLMapping = oTBLMap.Join(dSourceDatabase.Tables("[dbo].[" + myReader("tblToCompare").ToString.Trim + "]"), dTargetDatabase.Tables("[dbo].[" + myReader("tblToCompare").ToString.Trim + "]"))
                End Select
                '
                ' Retrieve Our Field Names
                ' 
                aFields = Split(myReader("Fields").ToString, ",")
                '
                ' Clear Out Old Comparisons
                '
                oTBLMapping.MatchingMappings.Clear()
                '
                ' Setup Our Comparison Fields Based On The Field Names Now Present In The Array
                '
                For I = LBound(aFields) To UBound(aFields)
                    oTBLMapping.MatchingMappings.Add(oTBLMapping.FieldMappings(aFields(I).ToString.Trim.ToUpper))                Next
                '
                ' Refresh Our Mappings
                '
                oTBLMapping.RefreshMappingStatus()
                '
                ' Setup our comparison session
                ' 
                oRedGateSession.CompareDatabases(dSourceDatabase, dTargetDatabase, oTBLMap)
                '
                Dim oBlock As ExecutionBlock = oProvider.GetMigrationSQL(oRedGateSession, True)
            End While
        Catch ex As Exception
            MsgBox(ex.Message)
        Finally
            myReader.Close()
            myConnection.Close()
        End Try

    End Sub