Navigation Error in MOSS

When I arrived at a client today I was told that the POC site was down. Pages would not load, the only pages that would load were the settings pages. On some sites the Quick launch bar displayed error links when I moused over the link the error was roughly

An error occured while rendering navigation. Context has expired and can no longer be used.

In the google sphere there is a few entries about this but not many solutions. One post http://social.msdn.microsoft.com/Forums/en-US/sharepointcustomization/thread/6a89c658-ab19-41a4-9875-8ff7c4d87c6a/ talked about workflow. And surely enough we were testing some workflow demos, but we had not attached any of them. However….my little helper did set up a policy setting on a document library after i left(which would have run overnight).

The short of it was I navigated via the site settings page to the document library that had the policy and I simply removed it. I did an IISreset to be sure then hay presto the site was back good as new. I dont know what caused it as I didnt look at the policy that was created, but if somebody could explain it then that would be great.

So if you get the above message another thing to try if nothing else works is to remove any information policies on document libraires (or content types)that were created before the error occurred.