I have an application that opens 8 RS232 com ports with VISA aliases. I am finding that under various circumstances the VISA references are not being closed (even though I am issuing a VISA close) The problem is that when I try to reopen the com ports some seem to be still open thus giving the error that the resource is valid, but VISA cannot currently access it. I have tried closing the com ports before opening and even querying the VISA driver to see which com ports it thinks are open and then trying to close those ports. But nothing seems to be fool proof. Was wondering if anyone has come up with a solution for this, thanks.