Troubleshooting: Error in MySQL Query
The system is set to automatically log people out after 24 minutes of inactivity. When this happens you will receive an error message.
Sometimes, you might be scrolling around on a page, but not performing any actions that would cause the system to load a new page -- thus, it might "feel" like you're being active on the page, yet the system might still log you out after the 24 minutes, and you wouldn't realize it until you received the error message.
If this happens, try "reloading" the page and see if that works (the system will likely require you to log back in when you do this... if it does, then that is a clear sign that you passed the 24 minute 'lack of activity" threshold.