Let me know if you find the cause, I have the same exact problem. I've tested all my cables and they are fine, but I too am using a Linksys BEFSR41. It doesn't happen all that often and doesn't affect my connection at all, just a little anoying when it pops up.
<A HREF="http://www.anandtech.com/mysystemrig.html?id=23900" target="_new">System</A>
<A HREF="http://service.futuremark.com/compare?2k3=2072215" target="_new">3DMark03</A>