TYPO3 Core

Here the error log:
2014-04-10 19:29:45 10.0.0.1 GET /typo3/null - 80 - 10.0.0.102 Mozilla/5.0+(Windows+NT+6.3;+WOW64;+Trident/7.0;+rv:11.0)+like+Gecko http://althoff-fam.de/typo3/backend.php 404 0 2 0

I also have disabled all extensions in localconfiguration.php and Cleared typo3temp.
The 404 Errors still occurs.

Did you also try the "Clear all caches" button in the Install Tool when all exts were removed? (it clears some more things)

Also "clear all chaches" in the install tool did not solve the problem.
The outcommend Extension was automatically ereased by Typo3. Only saltedPW is still enabled. See copied part of LocalConfiguration.php below:
'EXT' => array(
'extConf' => array(
'saltedpasswords' => 'a:2:{s:3:"BE.";a:4:{s:21:"saltedPWHashingMethod";s:41:"TYPO3\\CMS\\Saltedpasswords\\Salt\\PhpassSalt";s:11:"forceSalted";i:0;s:15:"onlyAuthService";i:0;s:12:"updatePasswd";i:1;}s:3:"FE.";a:5:{s:7:"enabled";i:0;s:21:"saltedPWHashingMethod";s:41:"TYPO3\\CMS\\Saltedpasswords\\Salt\\PhpassSalt";s:11:"forceSalted";i:0;s:15:"onlyAuthService";i:0;s:12:"updatePasswd";i:1;}}',
),
),

After I restarted the Server, I also went through all related Install tools again, but the problem with the 404 still appears.

Extensions are not disabled if you remove them from LocalConfiguration.php. Since 6.2 there a PackageStates.php file that contains all extensions in correct order and with a flag whether they are active.

Removing just the part from LocalConfiguration.php does not disable them, but deletes their configuration.

Hi Markus,
thank you.

I had to disable almost all additional extensions, bevor the backend was running fine.
Currently I don't know which Extension(s) the problem created.
Now I will enable them step by step.
If I should report the Extension, which creates the problem, let me know.

A possibility to disable the additional Extension via the install tool could be very helpful in cases like that.

Yes please report the extension(s) causing this. Post it here and maybe file a bug report also in the extension's bugtracker. Maybe such a ticket already exists.

The install tool automatically removes extensions that cause PHP errors. (Install Tool -> Important Actions)
If we find out why an extension is causing this, we might be able to extend the checks in the Install Tool to disable these extensions as well.

Finally I can confirm, that the vidi Extension, even in Version 0.3.0 creates the problem.
To disable vidi in the packageStates is not enough. It is also necessary to press the "Clear all caches" button in the Install Tool.