what is rpc_relay and why is it messing with my site code?

hi
just recently (48 hours?) ago a windows user of http://ourhomepage.com.au/ complained that they were seeing "rpc_relay.html" appended to some links on the site (the "category" links at the top of each page)  after they view the free lefora forum that's in a frame set at http://forum.ourhomepage.com.au/

I can only see this problem on MSIE (no probs in FFox or Opera on my linux box)

is this something to do with new social networking features or???  And can anyone suggext why it's messing with my session variables on the main site?

I'll remove the forum from the "frame set" anyway and see if that solves the problem...

thanks
brad