I've looked around the forum, and although there are some similar problems to this I don't think anyone has exactly this issue:
I had Win98, a 6210, DAU-9P (MBUS) cable and PC Suite 4.05. All was good until Windows 98 threw a big tantrum and I installed Win2K (everything else remained the same).
Now in Connection Manager, I am unable to change COM ports if I have selected DAU-9P (DLR-3P is fine). It says "Changing COM port failed" and it doesn't connect to the phone.
I can run LogoManager (http://www.logomanager.co.uk) with no problems, so the OS, cable and phone are all fine - it seems like PC Suite Connection Manager doesn't like Windows 2000 and DAU-9Ps. Annoyingly, the latest Suite, 4.06, doesn't seem to support the DAU-9P.
Any ideas, please? I would have real problems without this facility.