I have a problem with a classic asp page and I just cannot solve it since 3 days.
The page is working with Sessions - sometimes it happens that the ASPSESSIONID cook
Maybe later but could be useful as there is no accepted answer.
In application pool, at recycling options, check if you do not recycle your application too soon or you will ended with an ASPSESSIONIDXXXXXXX for each new application you respawn.
There are several recycling conditions. I set "minimum number of requests" to 1 by mistake and got an ASPSESSIONID for each request