Replace this:
With Me.lstOperationProducts
For Each vItem In .ItemsSelected
If Not IsNull(vItem) Then
strSet = strSet & "," & .ItemData(vItem)
End If
Next
End With
with:
strSet = ""
With Me.lstOperationProducts
For Each vItem In .ItemsSelected
If Not IsNull(vItem) Then
strSet = strSet & "," & .ItemData(vItem)
End If
Next
End With
' Remove the first comma
strSet = Mid(Trim(strSet), 2, Len(strSet) - 1)
Also, remember that if the item in question is Text, you will need to surround it with single quotes. So this line:
strSet = strSet & "," & .ItemData(vItem)
Would be:
strSet = strSet & "','" & .ItemData(vItem)
And the last line would need to be changed to:
strSet = Mid(Trim(strSet), 3, Len(strSet) - 2) & "'"
EDIT: I just saw you're also Diming the variable strSet as LONG. You can't do that, because LONG is an Integer. You have to Dim it as a String.