[plugin: buddypress] members/forums/groups.. doesnt work

hi
wp301 bp126
when i solve 1 problem, another problem comes in, instead, amazing.

now the blog itself seems to work ok but when i click on members/groups/forums etc in the menu i get error 404.

same with permalinks: now im using the default /p=? and it works but buddypress tells me to change it to something “prettier” so if i change to /%categoryname%/%postname%/ i get 404 error.

all the above is without .htaccess file. ONLY i change the permalinks, it tells me to put a certain .htaccess file but if i do, i get internal error 500

please advice
thanks