Why does this site doesn't open for me at times?

[nothingatall221b]

On some days the site works perfectly for me. But for most days, only the homepage opens and then clicking literally any link on there gives me an error message - be it forum, account, or one of the chat pages.

I have added a screenshot of error message. If anyone has some idea about it, please help me out. Mods, if you see this please provide some help.