Internal Server Error with PHP 5.5+

[EliaGa]

Hello everybody,
on my Plesk 12, choosing Php version 5.5 or 5.6 in hosting settings, I have an Internal Server Error page.
I tried to reinstall them from "add and remove" page, but problems persist.
Have you got ideas?
Thank you

 

[IgorG]

Not enough detail. Need more information. Error messages from logs, etc.