Same thing here. Happened about an hour ago. I am using Avast Free on Windows XP SP3. I chose "delete" and then restarted the system. After the scan, Avast found nothing suspicious. Now I got the same alert again. Seeing that others have absolutely the same error at almost the same time and regarding the same sfloppy.sys file, I think that is probably something wrong with Avast itself. Although it is strange, that after choosing "delete", the file is still there.
PS: Already did a virus check with Jotti, VirSCAN and Metascan. All sites say the file is safe and found nothing wrong.