Permission problems on upgrade


I am trying to upgrade my live site, but I get the message :

Warning: mkdir() [function.mkdir]: Permission denied in /var/www/vhosts/ on line 114

I have set permissions for the directory /core and the file fn.fs.php to 777, and but this doesn't help. I don't understand why this is happening, as i have upgraded my development site (which is in a subdirectory of my main site) and made changes to it, without any problems.

Any help much appreciated.



Sorted - I deleted the upgrade files in var/upgrade, and now it works.