i don't know how user permissions changed on the fly, but I do know this is a web server issue and should be brought up w/ your hosting provider. You can get them on the phone, right?

I agree with Scott, this is with 99.9% chance a server side issue and not so much a Concrete5 problem.

You disabled the cache in the meanwhile, didn't you?

I'd suggest you install eAccelerator (http://www.codeblog.ch/2009/06/concrete5-speed-eaccelerator/)... anyways..

Sometimes there's a limit of files and since Concrete5 has lots of files, you might have hit the maximum number of files. But I think this is unlikely because you usually can't even write a file..

Yeah given the fact that it happened to ALL of the installs on ONE box and none of them on another, its almost certainly something with the box's setup, not concrete5..

Call your hosting provider.

I think the permissions on files/cache_objects have been modified to where the server cannot write to them.

Delete files/cache_objects. The next time the page is viewed the directory should be remade, with the proper permissions.

If this doesn't happen, it may be that your entire files/ directory chain has lost write permissions. You'll need to "chmod 777 files/" if that is the case (and you'll probably also notice difficulty uploading files.)

My host sorted it for me, was just a caching issue, deleted and refreshed cache and now is fine :) Thanks mate