Well, I looked at the signature... it's certainly not ideal, false positives might occur on HTML pages that write about that piece of malware - but I wouldn't call this detection on the pagefile.sys necessarily a false positive, this signature certainly doesn't appear in an ordinary (unrelated) file.
You have to realize that the pagefile is a partial snapshot of the computer memory - so maybe you've visited some webpage covering this piece of malware... or it's also possible that this malware was indeed active in that operating system.
(Or, maybe you have a different antivirus installed in that system which keeps uncrypted virus signatures in memory...)
Personally, I wouldn't change this detection. (After all it's been there since April 2007, and I don't think it was reported as false positive during that long time... I can see one post about it here on the forum, and it was a conflict of 2 different antiviruses, as I mentioned.)
Btw, this isn't related to the beta in particular (any other avast! version would report the same)... so I'll probably move this thread into some other forum.