Since the latest version of Avast 19.3.2369 it is impossible to execute Autochk on disc C: - refused access to the disk, error (766f6c756d652e63 3f1). With previous version 19.2.2364 Autochk was OK. Avast had similar problem four years ago (at that time the problem was caused by Secure Virtual Machines (NG)).
Have you tried a clean installation of Avast?
There hasn’t been many reports on this and I can get it escalated assuming the problem is still there after a clean install.
No, I haven’t tried a clean installation of Avast. I tried only a repair of Avast. However, the problem persists and I have the same problem on two PCs. And you have tried to perform chkdsk of C: with the newest version of Avast 19.3.2369? Everything is OK?
Confirmed as per my post here: https://forum.avast.com/index.php?topic=225874.msg1498300#msg1498300
I can confirm this and yes even with a clean install of Avast. Besides the two machines I use that have the same problem with chkdsk with Avast, I also ask others and they also have the same results. Once the user uninstalls Avast, Auto chkdsk will work again as it should.
The problem evidently exists. I don’t believe that other users of the latest version of Avast (19.3.2369) have no problem with chkdsk. They just don’t know about it yet.
This bug has been reported and confirmed by the Avast team.
It is caused because of IDP and is reported under AV-19648.
I don’t have an ETA yet but when I get one, I’ll update the thread.
IDP = Behavior Shield?
Yep.
I have this problem on each of my systems and suspected it was AV related after searching for the error message. Uninstalled Avast and the problem went away. Is there a short term work around and if Behaviour Shield is implicated would disabling this work?
Hmmm, more than a week and the problem still persists. 
Disabling the Behaviour Shield temporarily before running the Autochk function on disc C: would probably work. However, if this is a much more frequent exercise running autochk it would be a bit of a pain. I would say would be better than uninstalling the Behaviour Shield component, which would be better than uninstalling avast.
Hopefully this would be a short term issue before a fix is found and tested to see it doesn’t impact anything else…
The fix is scheduled for next version (19.4) but Avast will also consider update for 19.3.
According to an Avast team member, they think the behaviour shield component must be uninstalled and a restart required. I haven’t been able to get a response from someone within the Behaviour Shield team for a precise answer.
Thanks for the clarification Alikhan.
+1 on those affected.
“Hmmmm, tricky…”
It appears (to me) not to be 19.3.2369 per se. It may be a dual problem with 19.3.2369 but with a Microsoft update influencing matters?
As I was still having too many problems, even with Avast uninstalled (autochk/chkdsk worked but the machine was still running badly), I put my backup on and was surprised to find I had 19.3.2369 before the backup. I thought I had (a) backed up, (b) updated MS updates (c) updated Avast in that order, but now it appears the other way round? My memory of the order in which I did things is at fault.
Checking logs, I updated Avast first, late Friday night, then set a backup going overnight. Then I did a bunch of MS updates on Saturday, see .png attached - note I excluded the two Mar 2019 updates.
The problems started after that and I initially suspected Avast due to the Autochk issue, as it seemed those MS updates wouldn’t be messing with the disc at a low level. I removed Avast and Autochk/chkdsk worked. But then the machine was still very slow so I put the backup on.
So I think 19.3.2369 is part of the problem, but it may need one of the MS updates to reveal it. I’m now on my post-19.3.2369 and pre-MS-updates version and the machine is fine (touches wood)
Thanks
W7 Pro 64 bit
I’m having exactly the same problem with both Avast and AVG starting with the latest release. Uninstall the antivirus and chkdsk /f works, install the antivirus and chkdsk /f doesn’t work.
Same problem with Autochk/chkdsk… I my case I found this problem in a very problematic way. My system drive (C:) filesystem was marked dirty due to a power fail, after which it was not possible to restart normally because chkdsk could not run and I couldn’t reach Windows to uninstall Avast.
Terrible experience, ended up loosing a lot of time to circumvent this startup situation, uninstall Avast and finally be able to run chkdsk.
This needs to be fixed and I’m a bit surprised there still isn’t at least a patch or clear instructions from Avast how to resolve this situation.
(I did report the bug through Avast interface before anyone asks.)
Last two posters - have you recently done any MS updates? Interesting the problem appears with AVG as well
Considering that AVG is now part of Avast Software and some of the underlying functionality will be the same.
If that has been triggered by MS updates in win7 I wouldn’t know.
But as Alikhan mentioned:
Since Avast 19.4 is in beta testing, hopefully that won’t be too long before release.