If the file you checked matches the location of the file detected by avast, I have just checked mine and no detection. So not even avast detected it on VirusTotal and Jotti ?
The last update was very big so it is possible, but it is strange it doesn't detect anything in my XP version of taskmgr.exe.
If you are getting a virus warning that you believe is a false positive, then if you can zip and password protect ('virus', will do with the password in the email body) the suspect file and send it to virus @ avast.com (no spaces), or you can also send it from the avast chest (select the file, right click, email to Alwil Software). No need to zip and PW protect when the sample is sent from chest.
Give a brief outline of the problem (possibly a link to this thread), the fact that you believe it to be a false positive and include the password in the body of the email. Some info on the avast version and VPS number (see about avast {right click avast icon}) will also help.