Piranha CMS caches a lot of meta-data for performance and to minimize the round-trips to the database. The site information, as well as the sitemap is two of these things as these will most likely be used in every page-rendering.
The default cache implementation uses the IIS cache, which is per application pool. The cache is invalidated when data is modified in the manager interface, but if you for example would run the manager interface in another application pool (site/application) this will make the caching fail, causing the kind of errors you describe.
Not being sure how your application is set up, this is my primary guess. If you are in fact running the client web & the manager in different application pools, and you need to continue doing this you should try one of the following approaches.
- Implement a distributed cache provider
- Set the system param
CACHE_SERVER_EXPIRES
to 1
Setting the param to 1 invalidates all server cache after one minute. This is of course not to recommend if you are expecting a lot of traffic to your site as it will more or less disable the caching mechanism.
I hope this helps you.
Best regards
Håkan