This is what i get when click on category

[Bebrona]

After i added one extra category i got this in frontend, before adding the category all worked fine.

[federica]

You can try to look the first topics in the "bug" section, they could be help.

[Bebrona]

I can't find a solution in the bug section. 

[federica]

Ok, if you can't find a solution it is necessary proceed with debugging
Can you post the php error log related to the crash? Only the lines related to this error, not entire file, please.

[Bebrona]

As soon as i add a category and i need to change the order of the category in backend it messes up the categories in frontend.

So i don't dare to add any categories any more.

[federica]

Bebrona, post the php error log related to the crash please. The error log file is useful to do a debug.

[Bebrona]

Where can i find it?