You should never turn off your AV, for your machine is unsecure then!!!
HDW
I also does not agree with this 
Consider the following (similar, but not identical to the author's thread) scenario (where avast had to be completely uninstalled in order to provide basic maintenance to the computer?!)
A computer (Win7 32bit with up-to-date Avast running Ok, no viruses) was slow.
Hard Disk Sentinel reported vast amount of bat clusters on the hard drive.
The solution: run a ChkDsk utility on that drive.
However, when ever I attempted to schedule ChkDsk after the system restarted - ChkDsk failed to run with the exit message: this disk is locked due to unknown utility?!?
Mbam was then run on that system and Mbam found NOTHING.
After 3 whole days I figured it out:
(Accepted solution)
- Unnistall Avast from that computer. Completly!
- Run ChkDsk (ChkDsk worked then OK!)
- All bad clusters were mapped.
- Install Avast from scratch and let it update.
(Worked OK)
Why Avast on that computer was locking the drive and preventing the ChkDsk to run - newer actually figured out.
Supposed answer: Avast files itself were maybe damaged due to the bad clusters on that drive.
In that (possible?) case - Avast overlapped with ChkDsk or something, preventing tha ChkDsk to run.
I wonder if the
Avast Self Defense Module might be the culprit
Try unchecking the box as shown in the screenshot and see if that fixes the problem.
