Deleting Spam - Fatal Error

Dear Expert,

I just got my first (most probably) spams. As I tried to delete (or mark them as spam), the system ask me to confirm the process. As I confirm to delete the accounts, than I got fatal error message:

Fatal error: Using $this when not in object context in /home/sinauo5/public_html/ on line 1053

What is going on, anybody can help?

I'm using WP 3.0, multi-site, BuddyPress the latest and quiet a number of plugins (but no anti-spam etc.).