Error 500 ! All links dead ! Correct PHP and SQL!

Hi Guys,

i was really excited reading about community builder and installed it right away. The whole installation went fine and checking the dataabase (under tools) works too, everything green. I followed the instruction after downloading and set up a menu item and so on, this works fine too. But when i try to click a link, for example the mandatory link item or the registration form, i always get error 500 (HTTP-Fehler 500 (Internal Server Error) in german

I read a lot about a wrong PHP or SQL version, but i checked both! I turned of SEF in Joomla but it still doesnt work. Tried to reinstall, same problem

I dont know what else to do, can anyone help???

I have the same problem, but only on my local server, on live site there is no problem. So I think there is some problem in localhost server (I am using XAMPP apache server) or PHP settings, but I dont know exactly where...