[TYPO3] No Extension for import in Extension Manager

[Nils Meyer]

Hi,

I am using typo3 4.0.1 (freshly installed 30 minutes ago). When I try to 
import an extension from the TER, the Extension Manager doesn't find 
any. I have so far checked the following things:
1. the extension repository in typo3tmp/extensions.xml.gz is up to date 
and contains a list of extensions
2. Enable extensions without review (basic security check) is checked
3. show obsolete is checked
4. the memory limit is not exceeded by the extension manager (set to 
64MB just to be safe)
5. other Typo3 Installations on the same server are working (including 
extension import).
6. There are no errors reported in the PHP error log.

Even when I enter no search term (so it should show me every extension 
available) it returns "*No matching extensions found.". What else could 
possibly be the problem?

Nils