I fumbled around with an ancient T3 installation (tried an upgrade from 4.5 to 6.2) and before the fumbling created a backup from the entire directory on the webserver as well as the database.
Now I tried to re-activate that backup (a.k.a. 4.5). The install tool works fine, DB-Connection seems to be ok, but when I try to access the backend, it tries to access /typo3/sysext/install/Start/Install.php which isn't present at the described location.
I tried to delete all caches, emptied the typo3temp folder - nothing helps. It seems there's something stuck from the upgrade process, but I have no idea where.
Any ideas?
The Problem's solved. T3 6.2 uses the PHP Opcode Cache which can't be reset in the 4.5 install tool. Something must have been stuck there. I wrote a little PHP script that clears the cache and viola, it worked.
opcache_reset();