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mwac.sys listed as cause for BSOD Win Vista 64

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MB Premium 3.44 updated to 3.51 8-15-18

Win Vista 64 SP2 - AMD Phenom II x4 920 MBO 8GB - ATI Radeon HD 4600 Series (MSI) 

Samsung SDD 1TB 

All of a sudden multiple BSOD with v3.44 several times an hour calling out mwac.sys even after updating to v3.51.

Finally out of desperation, I completely uninstalled MB which seem to solve the problem. No BSOD for 14 hrs. But I am now not running any virus/malware protection. Have not reinstalled.

Please advise on course of action to get MB up and running again WITHOUT BSOD would be nice....:)




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Driver verifier can run for 24 to 48 hours - it depends on the situation and the system.
First try this: 


I put it in a code box because the link directs to the first page - and this post is on the 3rd page.
Here's the direct link for the beta: 


Good luck!

Edited by usasma
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Thanks John.

After disabling MS Verifier:

1. Downloaded as per link above

2. Rebooted

3. While attempting to install above received error message. "This OS not supported". I am running Vista Home Prem. 64 SP2.

4. Open to suggestions. Starting to look like MB will no longer support Vista. Perhaps I should just a reinstall of 3.44.or 3.45 and rerun MS Verifier. Where can I find earlier versions that were Vista compatible on the MB website?

Btw, I'm running a 3 x boot system on separate HDs with Vista 64, Win 7 Pro 64 and Win 10 64 Pro with MB 3.44. No such BSOD problems (yet :)

In the meantime with MB not running Vista OS using Chrome and/or Firefox rock solid. The problem seems to originate only when running one or both of those browsers while MB us running (with real time protection)...

Because neither Chrome nor Firefox support Vista, I guess I'm stuck with Chrome Version 49.0.2623.75 m (64-bit) and Firefox 49.0.

I am using Vista because I have a legacy video editing program and proprietary GPU card from Matrox and about 50 other programs that are installed for filmmaking etc.

Guess I just have to finally byte the bullet and do a total migration to Win 7, where I have already installed the Matrox drivers and Premiere Pro, PS etc.as I'm assuming the above MB UG is compatible with Win 7, along with Chrome/Firefox latest versions(??)... Personally not entirely sold on Win 10 yet :)

Suggestions anyone?



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Update 08-16-2018 @ 5p PDST:

Decided to reinstall a much earlier version of MB (PKG vers 1.0.0 UG PKG vers 1.0.0) which I had downloaded in 08-23-2017.

Resurrected the activation code and Premium is up and running. At least I have some protection now. Real time Web Protection ON

I'm current running without MS Verifier.

I'll report back if I get BSOD related to MB...or not :)


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I’d think that the folks on the MawsreBytes 3 forum would be the ones to suggest Vista compatible versions

try disabling web protection - that’s the most common thing that seems to workaround the problem (that I’ve seen)

ive been running W10 since it first came out - and have had few problems with it.

Good luck!

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An update:

After reinstalling MB 3.1 I ran for just a few hours with Web Protection toggled ON when Chrome crashed.

Here's the Who Crashed Dump Analysis:

Crash dump directories:

On Thu 8/16/2018 9:38:49 PM your computer crashed or a problem was reported
crash dump file: C:\Windows\MEMORY.DMP
This was probably caused by the following module: ntkrnlmp.exe (nt!wctomb+0x189C4)
Bugcheck code: 0x50 (0xFFFFF900C2F34270, 0x0, 0xFFFFF96000270BD6, 0x0)
Bug check description: This indicates that invalid system memory has been referenced.
This appears to be a typical software driver bug and is not likely to be caused by a hardware problem.
The crash took place in the Windows kernel. Possibly this problem is caused by another driver that cannot be identified at this time.

After BSOD I rebooted and ran MB with Web Protection OFF. After about 16 hrs. NO BSOD.

Seems to be connected to Chrome/Web Protection.

I'll continue to run with Web Protection OFF. Too bad. Looks like any version of MB running on Vista before the most recent version(not compatible with Win Vista) is subject to BSOD as long as Web Protection is ON..

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OK. I can with about  90% certainty report that running MB with Web Protection OFF seems to alleviate the frequency of BSOD. I'll have a higher sample rate in a week or so. Especially after opening/closing Chrome browser (v 49).

One interesting revelation:

I was loading a program called SpeedFan which monitors the temperature using digital sensor on MoBo, including CPU core, GPU HDs and allows for controlling the cooling fan speed/duration with  config script on Start-up. There are a number of command line switches that apparently can be used to suppress monitoring...probably because of the  IRQ conflicts with some MoBo's.

On a hunch, Googling SpeedFan BSOD turns out there known problems with some MoBos incl. mine AMD. Not compatible with South Bridge...sometimes caused BSOD.

I no longer run SpeedFan to continuously monitor temps. I now invoke, check the temps etc. then close immediately. Or use Speccy to check tempts. This program, SpeedFan.sys (3.52 most recent) may have been contributory...or not. Dunno...but I'll keep it from running continuously.At least I can use the computer now.

As of several hours...no BSODs (win2k.sys listing offending file) after opening/closing Chrome on Win Vista...

Hope this helps someone.



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Just in case you needed it, the last version compatible with XP and Vista along with info about it can be found in this FAQ entry.  The last supported version for those operating systems is Malwarebytes 3.5.1 build 2522 component package 1.0.365.

As I understand it, they do still pan to fix any major bugs that should crop up on the older operating systems as long as they are still supported, so if this turns out to be a bug in the latest release then it should get fixed with an update at some point.

Edited by exile360
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