BuddyPress

I have another site with a current multisite install, using that exact permalink structure with absolutely no problems. These issues only happen when activating BuddyPress. Once it’s activated, the only […]

I checked all your suggestions. The problem persists: You can see what is happening at:
http://www.preview-classes.com

1) Looks like I mistyped the permalinks settings in the forum post: It actually reads: […]

Thanks Aces, but Problem persists with your suggestions:

1) htaccess shows:
RewriteEngine On
RewriteBase /
RewriteRule ^index.php$ – [L]

# uploaded files
RewriteRule ^([_0-9a-zA-Z-]+/)?files/(.+) […]