Outlook pst file effects Windows credentials

[NYCBroadway]

I have a problem more with Outlook 2003 client on XP that causes
Windows credentials to expire. I copied a few pst files in the 2002
format locally and pointed to them in 2003 Outlook client. Now every
day I get the pop up window to enter password into Outlook and then
have to relog on to renew Windows credentials as well.
What in the pst file can possible be doing it?
I do not of any passwords associated with those pst files. If I convert
them to 2003 format will that help?

Thanks.