Error 500 Internal Server Error in web GUI

I am having a problem on 3 separate Fortigate 200Ds. I can log into the web interface, then it loads for about 30 seconds and displays "Error 500: Internal Server Error" in the left pane. The main section on the right is just blank. I can SSH into the firewalls, but they are sometimes slow to give me the initial prompt after login. There are no processes taking up more that 5% or so of the CPU. I have tried updating the firmware to 5.2.3 but I still have the problem. I have seen related bug reports that claim to have been resolved in firmware updates, but I am on the latest firmware. I have a hard time believing I am the only one seeing this since it's happening on 3 separate devices. So far the only fix has been to power cycle the units. Has anyone else seen this?