Looks like the Avira engine is having problems handling the file referenced in the mwg-core.errors.log.
Do you have a corresponding entry in the mwg-antimalware.errors log file? If so, it should have an error ID that comes from the Avira engine itself.
In Error Handler -> Default -> Block on Anti-Malware Engine errors, do you have a rule that handles Error.ID equals 14002?
You could whitelist the destination site, configure MWG to fail open for Error.ID equals 14002, ask support to verify that the download isn't infected, etc.