Keep getting this threat

Every time my screen saver scan runs I get a Win32:malware-gen infection notification. Also a Win32 dropper-gen infection notification. Why does this keep coming up if Avast keeps removing it. Do I have to do something else. I also ran malwarebytes anti-malware quick scan and nothing comes up. I have 64bit os so I can’t run boot-time scan. Is that necessary? Also when i try to delete infection from chest sometime it deletes it other times it says Error:SYSTEM CANNOT FIND FILE SPECIFIED. This is a bit annoying how do I keep this from constantly happening. Also can I still back up my computer with this infection continually popping up?

Which is the screensaver?
Can you submit the file to www.virustotal.com and post back the link to the results?
You don’t need to delete the file from Chest… let it there.

I also ran malwarebytes anti-malware quick scan and nothing comes up.
Did you update Malwarebytes before you scanned ?