fishy said:
Hitting the 'theme' button fixed it yesterday, but it came back today. The theme button fixed it again.
I'm guessing that maybe there's no default theme set, as part of the warning message is something about a config.php file not existing.
Yeah, the sp_green style referenced in the error msgs in the screenie you posted (thanks for that, helps a lot!) hasn't existed since last september so I'm a bit confused as to how it's still around in your browser's cookies!
There is a default theme set, but for some reason that value must have been getting retrieved from your browser's cookie and overriding it with a non-existent them. I've added some code to catch any more problems like that, so should be ok from now on.
I also believe this is the same issue Muhnay experienced when he was using Opera - I should have twigged from the error message but obviously didn't look closely enough, sorry!