Hey,
Just did an upgrade on our test server from Jira 4.1.2 to 4.4 (on route to 5.2) and it seems to have gone OK so far except for a couple of little things like this.

As you can see, every tab in plugins shows that error at the top (not immediately, the tab loads for a couple of seconds then the error appears) and no plugins are being displayed from the Plugin Exchange wher ethey should be at the bottom there. I just see a loading spinner for a second then nothing.
Anybody have any ideas?