TYPO3 Core

I can not confirm that. Did you run a db-compare (install tool)?

DB-compare has been executed. No difference is shown here.

Import the static data from sysext "em" and maybe clear the user-settings.

This is what steffen always sugested me (and helped). Make sure that afterwards you have the TYPO3.org repository entry in the EM settings (it comes from table sys_ter and has to contain 1 entry).

There is only 1 record from the "em" which has already been inserted by the Install Tool.

sys_ter:

INSERT INTO sys_ter VALUES ('1', 'TYPO3.org Main Repository', 'Main repository on typo3.org. This repository has some mirrors configured which are available with the mirror url.', 'http://typo3.org/wsdl/tx_ter_wsdl.php', 'http://repositories.typo3.org/mirrors.xml.gz', '0', '0');

Does it work already, or still not working, Franz?

This is a working site since many years and with many TYPO3 versions already used before.
However now the EM does not work at all.

I have just made an update to the latest TYPO3 trunk. Still a broken EM.

Please have a look at Firebug's network panel. What's the content of the XHR?

I can confirm the message.

But for me it shows up in the "Remote Repository" tab only.
According to the line in the upper right corner there should be a fresh and updated repository list with 4883 extensions, but actually the list happens to be empty.

As soon as I try to find any extension by the filter, the message pops up.

Without any further error message (inside request) i can't do anything, it's working now on most installations without problems.

I'm new to TYPO3 and had a rather stupid setup where this problem occured. I had nested .htaccess files with rewrite rules. When I removed this the extension manager worked again.

Background:
I installed the introduction package in the root directory of a domain. I didn't want to delete it when installing a fresh installation for another tutorial. So I used a subdirectory for the new installation. In both directories I had a .htaccess with rewrite rules. When I deactivated rewriting in the root directory of the domain the EM in the subdirectory worked again.

BTW: This rewrite setup also caused login and login expiration problems. I read a two year old thread where Franz had the same problem. Typo3 created two cookies for every value. One with the path / and one with /subdirectory. (I cleared cookies all the time and only used the installation within the subdirectory.)