[TYPO3-bugs] Error after upgrade to Typo3 4.2.8

[Raf]

Hi,

I upgraded from 4.2.6 to 4.2.8 and have some errors in the backend: When I
try to login I have: Cannot find tslib/. Please set path by defining
$configured_tslib_path in index.php.

And if I set the path manually I have an other error telling me that it 
could not find the localconf file then that the cms
extention is not loaded!
That's very strange.

Somebody have that kind of errors?

Thanks a lot!
Raf