WordPress MU

has anyone got that error?
everything works fine
except plugin activation ine site admin menu
the complete error is:

ERROR
The requested URL could not be retrieved

While trying to retrieve the URL: http://blogmerkezi.com/wp-admin/wpmu-edit.php

The following error was encountered:

* Zero Sized Reply

Squid did not receive any data for this request.

Your cache administrator is sysadmin@sabanciuniv.edu.
Generated Sat, 18 Aug 2007 19:25:27 GMT by squid2.sabanciuniv.edu (squid/2.5.STABLE7)

regards

Turn off squid for that site. Your current squid config is not set up to work with wpmu. WPMu has a built in cache anyway. Do a search for 'object cache' to see a thread on the topic a few days ago.