Sorry for bumping this old thread. I got this error twice
The following error occurred:
An unexpected database error occurred. Please try again later.
I have opened a new window and I have only one tab opened www.trucksim.org. When I am away from the browser the forum automatically refresh and thats when the error appear.
I am using latest version of Mozilla Firefox 38.0.1 and Ad-block is disabled.
How long were you AFK for? If you are AFK for about 8+ minutes (I think), the forum will log you out but since you were in a different tab, the browser would think that you are still logged in and would try to fetch something that only registered users can access like the user comments in the library.