Eclipse: Error retrieving "feature.xml". [Error in opening zip file]

My problem:
whatever I try to do under "Help/Software Updates/Find and Install", I get this immediate Error Message:

Quote:

Error retrieving "feature.xml". [Error in opening zip file]

The same problem is described in:
http://www.myeclipseide.com/PNphpBB2-viewtopic-t-12732.html

The solution:
Just delete the site.xml file under the eclipse folder! I actually renamed it to ~site.xml and after the installation was complete I renamed it back and restarted eclipse. The reason was that the site.xml contained references to the SVN plugins that I needed. Why the site.xml causes trouble, no idea.

Background and what I am currently doing:
My current project is to help finocom write a call center software that is multi client and clustering enabled. For this I need to write some php code and rails code. I installed eclipse 3.2 with aptana studio as eclipse plugin installed. For my php coding I wanted to have some syntax highlighting for php and therefore wanted to install the php plugins of Aptana.