avast-fss question

I am seeing following in syslog:

avast-fss: Unexpected AV SCAN response code (451)!

But I am not sure what is the meaning. Any ideas what is the reason this message?

Hello,
the logging sucks; this is a generic error code, the actual code is not being logged. Fss package scans files asynchronously after they are reported as changed. It often happens that eg. the file is deleted/moved before this can happen, thus scan fails and log gets flooded by these messages. If we release a new version of fss, we will try to make it less verbose.
Kind regards,
Ondrej Kolacek