Probably, when you set a tab with code it calls the click event again ( and again, and again, etc. ), which is why you get an Out of Stack Space error.
Try this:
Private Sub TabLTATran_Click(PreviousTab As Integer)
Static Skip as Boolean
If Skip = True Then Exit Sub
If CheckValidEmp = False Then
Beep
txtErrMsgBox.Text = "Please Enter A Valid Employee Number!"
Skip = True
TabLTATran.Tab = PreviousTab
Skip = False
Exit Sub
Else
txtErrMsgBox.Text = ""
End If
End Sub
Robert