[Solved] Frontend does not display - Can't log into backend

[BravoNet]

I was working on a site, and everything was working fine. Then suddenly when saving a page in the CMS, I was logged out and the site can not display 

Frontend displays:

Warning: fread() [function.fread]: Length parameter must be greater than 0 in /home/www/designfunktion.bravonet.dk/lib/classes/class.contentoperations.inc.php on line 515

Backend/login displays:

Warning: Unknown: write failed: No space left on device (28) in Unknown on line 0

Warning: Unknown: Failed to write session data (files). Please verify that the current setting of session.save_path is correct (/var/lib/php5) in Unknown on line 0

Can someone tell me what happend and how I get back on track?

[BravoNet]

This is the web site: http:// designfunktion . bravonet . dk/

Anyone? please...

[BravoNet]

I didn't do anything - but now the site is working again - spooky.

I think I'll make a backup