This problem gives me Deja vu. I run a forum built on SMF and host it on GoDaddy. I had very similar problems. It took awhile to figure out that it was due to a lack of a firewall that permitted AI bots to constantly attack the site. This activity would, over time, cause GoDaddy to throttle the site and it would eventually exceed capacity and force the site down. Paying a little more to add the extra security prevents the bot attacks and there have been no site outages since.

It was not presenting for some days to me, but now you are right and it is happening again. 

The problem is not happening now for some days.
Is it solved? What did it cause?

I am still experiencing this issue, unfortunately.

The intermittent nature of the problem definitely indicates a server-side issue.
Maybe there is a connection pool issue--some crusty old code not disposing of connections appropriately, perhaps?
Could be disk usage is being thrashed...though it seems that wouldn't be likely to give an immediate error response unless the problem has been bad for a long time.

Ironically, I just got that SMF error when I tried to click on this post. A refresh fixed it. So yes im seeing the same ha