Re: Forum got installed, but I can’t read any posts!
It has nothing to do with incompatibility between versions; totally unrelated.
There are two methods there to get permalinks working.
1. Options +Multiviews (works for some people)
2. Access http://www.example.com/bb-admin/rewrite-rules.php with a browser, then grab the displayed text and paste it into your .htaccess file.
If you tried the first method and you got an internal server error, it sounds like the host does not allow that in an .htaccess file. Try the second method. If that doesn’t work, you might need to contact your host to see what’s allowed.