You needn't bother. It's an error caused by an unrecognized filetype. This triggers errors in many AV programs where there actually is not virus.
The file you went looking for is invisible, and that's why your could not find it. It's invisible for a reason, so you won't mess with it.
You should get rid of Sophos. It isn't needed. There are no known viruses affecting OS X.
Helpful Links Regarding Flashback Trojan and Virus Protection
That file stores an older version of Safari following an update. Most likely, you were infected with Flashback at some point and the infected copy of Safari ended up archived in that file. If that is the case, Sophos will call the malware OSX/Flshplyr-X (where X is some letter). In any case, though, there's no need to worry... whatever's in there can't hurt you, as long as you don't expand that file and try to use the version of Safari it contains, and eventually it will be replaced by a newer version of Safari by another update.