I'm getting a similar error when I try to access the first Group that I have created.
URL: <domain.name>/community/grp.php?action=group&ID=1

Message:
Warning: file_get_contents(<domain.name>/community/groups/orca/?action=group_last_topics&forum=Website&trans=1) [function.file-get-contents]: failed to open stream: HTTP request failed! HTTP/1.1 500 Internal Server Error in /home/thejourn/public_html/community/inc/classes/BxDolGroups.php on line 419

I got the error message see more with 6.1.0 and also with 6.1.1

I've checked my phpinfo.php page and can see that allow_url_fopen is On.

Any other ideas?