Log in problem to XLA add-in file

Alright people, a bit of a strange problem here. Can't find anything on the web about this, so I've signed up here hoping that one of you can help

Our organisation is currently upgrading the network OS from Windows 2000 to Vista. One of the users has a .xla file that they access in Excel, using a username and password. Now before you think it's something to do with breaking the password, it isn't.

The problem is that since changing over to Vista, the username and password (that we know) is being rejected with a bad password error. The file can only be opened when you are logged in as the the user on the old Windows 2000 PC. I've tried logging in as myself to that PC, and cannot access the file using the username and password. This makes the problem seem like it is profile specific.

My question then really is, how is this possible? Can you tie the specific user to the file as well as password protecting it? Is there a specific registry key that needs to be copied to the new profile on the new Vista PC, or any other specific files from the users profile?

I can see the code in the XLA, if that's any help.

Thanks for you help!