Got the same problem: Session vars disappear!
Using trace="on", could see session vars on page load but on post back all session vars gone! Didn't show up until switched from asp.net 1.x to 2.0
Took awhile but I did find the cause. Not in the vb
source code...it's in one of the asp:image... tags! Two ways to fix or work-around:
1) Remove or comment out asp:image tag
(just ones with missing imageURL should do)
2) Add imageURL="valid link" to asp:image tags (if missing)
To test, deleted almost all code in the code behind. Except for setting about 5 session vars on page load and one in post back.
I didn't try imageURL with an invalid link to see if that blows-up all the session vars too, geez, I hope not.
In original asp.net 1.x version the imageURL fragment was set in code. At design time, the imageURL was left blank. This didn't affect the session vars as it seems to do now under asp.net 2.0
If I may politically digress, hasn't someone read you the book 'The Earth is Flat'...Session Vars CAN'T DISAPPEAR...you're wrong!!!!
I've noticed this is one of several problems that seem to have no solution...;)