As you can see from the title, our output cache is not working. We only recently noticed but it did at one time work (verifiable with a hidden timestamp at the bottom of the page; we cache for 3600 seconds using
varybyparam="*"). We attempted to isolate the piece of code that is causing the problem (either the page is not entering the cache, it is immediately invalidated, or the key used to cache it is unique and the cached page can't/won't be found) and it turns out that when we commend out this line:
from a cookie-class that caching starts working perfectly!
We're not sure how long caching hasn't been working but the suspicion is that a Microsoft Windows Update slipped through QA. We have verified on an older, un-patched virtual server that output caching works perfectly (although the environment isn't 100% like our production so there's some doubt in there) and that we don't need to make any changes to our code to get it to work. Only on our production servers (Win2k3, x64 but app pools running in 32bit mode, IIS 6, .Net 2.0) do we experience this problem.
Days of googling only turned up references to output caching breaking for SharePoint after MS11-100 was applied. We've hit a brick wall and have contact Microsoft Support but was wondering if anyone in the community has run into this issue, something similar, or just has ideas about how to fix.