Open transaction in SAPgui

I want to display a transaction such as MM01 in SAP gui from Visual Basic. I tried to use function RFC_DISPLAY_MATERIAL_MASTER (without any parameters), but it works only in ABAP debugger. Without debugger, it returns SYSTEM_FAILURE.

Here is the code:

...

theFunc = functionCtrl.Add("RFC_DISPLAY_MATERIAL_MASTER")

returnFunc = theFunc.Call

If returnFunc = True Then

Return 0

Else

callException = theFunc.Exception

Return -1

End If

How about transaction such as SD62(change order bom)? I couldn't find RFC-function to display it. Is there a general function to display a transaction in SAPgui? RFC_CALL_TRANSACTION seems to do it only in backround.