Think someone can fix that...?
I think someone edited some code they shouldn't have,
Admins, I'd recommend installing a new version of phpBB in another folder, and making it reference the same database after installation, then renaming this current phpBB folder to something like oldforum63463 (so it can't be accessed), then renaming the new installation to forums.
If it's not a coding error (causing too many SQL requests for example), then the forum simply needs a better server.
But that said, the most users ever online on this forum is 45, and there are currently 13 online.
There's just no way that is too much for the server to handle, which is why I'm leaning towards heavy coding edits being the cause of the problem.
It's always a good idea to ask over at phpBB.com, support from them is prompt and free.