System.InvalidOperationException: Cross-thread operation not valid

[Dave Sell]

All,

I have a main VB form (frmMain). frmMain has-a subForm (frmOPC), and declares a private member of type frmOPC WithEvents.

' frmMain
Option Explicit
' ...
' This is my SubForm which can Raise an Event
Private WithEvents m_frmOPC as frmOPC

I wish frmMain to respond graphically to an Event Raised by frmOPC, such as update a frmMain.Label.Text = "something" when frmMain captures an Event Raised by its subForm, frmOPC.

Private Sub m_frmOPC_OPC_DataWriteVerified(ByVal intLaneNum As Integer) Handles m_frmOPC.OPC_DataWriteVerified
    ' Do something interesting on the screen ...
    Me.lblOPC_Result.Text = "Lane " & strLane & " data verified (" & strTime & " mSecs)."
    ' This causes an error!
End Sub

The SubForm has-a VB6-developed ActiveX control which Raises an Event.

' frmOPC
Option Explicit
Imports ActiveX_Library
' ...
' This is my ActiveX Object which can Raise an Event
Private WithEvents m_OPC_Process As ActiveX_Library.OPC_Process.cls_OPC_Group

Obviously, when the VB6 ActiveX Object Raises an Event, I capture this Event, and in turn, Raise my own Event:

Private Sub m_OPC_Process_DataChanged(ByRef Context As String, ByRef TagName As String, ByRef TagValue As String) Handles m_OPC_Process.DataChanged
    RaiseEvent OPC_DataWriteVerified(m_intLaneNum)
    ' Notice, the frmMain is trying to update it's screen right now I think, before this Event has finished...
End Sub

The problem? I'm glad you asked! frmMain will puke a hard-to-track-down error if I try to mutate an object on the Form:

System.InvalidOperationException: Cross-thread operation not valid: Control 'lblOPC_Result' accessed from a thread other than the thread it was created on.
   at System.Windows.Forms.Control.get_Handle()
   at System.Windows.Forms.Control.set_WindowText(String value)
   at System.Windows.Forms.Control.set_Text(String value)
   at System.Windows.Forms.Label.set_Text(String value)
   at RUUD_Production_Supervisor.frmMain.m_frmOPC_OPC_DataWriteVerified(Int32 intLaneNum) in E:\Work\Visual Studio 2005\Projects\RUUD_Production_Supervisor\RUUD_Production_Supervisor\frmMain.vb:line 188

Interestingly, I can do anything non-graphical with no issues. The error is only thrown when I try to make changes to the Form's screen Objects.

I found a workaround, which is always green squiggled as a warning in the IDE at design-time, but effectively removes the erroneous behavior (no error is thrown):

Private Sub frmOPC_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    '
    ' ...
    Me.CheckForIllegalCrossThreadCalls = False
    '
End Sub

I include a screenshot of the green squiggle tooltip/warning.

I am looking for ideas and suggestions for a better solution to the problem than my work-around, if one exists. Questions for clarification welcome.