Can you provide the code where this error is occurring?
I have done past experiments with ASP <-> ASP.NET interactions and found that you need to manually hand information back and forth thru the querystring or well defined cookies. My tests showed that they will not share session information (as they shouldn't because they are two different processes even if they are running in the same virtual application directory). I'm not sure how you have been able to make this work when it has.
-
Peter