Avast! Antivirus causes BSOD on Windows 7 beta
Today I fixed a new problem with my test installation of Windows 7 (first public beta): Avast! Free – my “default” antivirus, was causing random system crashes. After some tries, I understood that blue screen of death was occurring during internal network activity. To be more precise, the problem is located in the use of shared folders (aka “samba shares”, for Linux users) and it involves the tdx.sys file, that seems to be often a protagonist of BSODs.
I suspect that this problem is not directly bound to Avast! (in any case this can’t be considered a bug of the application because Windows 7 is in beta status and so isn’t officially supported by Avast! Antivirus) but to the drivers of my network card, as seen in my previous post about connection problems with Live Messenger.
The fix was simply to uninstall Avast!, replacing it with another free antivirus: Avira Antivir, that seems to run smoothly without any problems, also on Win 7.
Now I’ve to solve my last-big-network-problem with the new operating system from Microsoft: I cannot access shared folders and printers from a Mac Mini of my LAN. No problems with Vista, no problems neither with Linux (and shared folders are using SMB protocol from Microsoft!), but nothing to do with Windows 7. Stay tuned 
January 23rd, 2009
To access shares on your Mac from your win7 you need to edit your registry:
Start>Run>secpol.msc [enter]
Click on “Local Policies” –> “Security Options”
Navigate to the policy “Network Security: LAN Manager authentication level”
and double-click it to get its Properties. By default Windows Vista sets
the policy to “NTVLM2 responses only”. Use the drop-down arrow to change
this to “LM and NTLM ? use NTLMV2 session security if negotiated”.
• Naviate to the policy Network security: Minimum session security for NTLM SSP based (including secure RPC) clients, double click and make untick Require 128-bit encryption
January 23rd, 2009
Thank you very much, it worked!!!
January 25th, 2009
I’ve spent days trying to work out this tdx.sys blue screen I’ve been getting in Windows 7, and I only wish I’d found this post earlier
As it happens, I thought it was to do with the wireless networking, as the OS runs perfectly with wireless disabled (and I hadn’t tried wired). I finally found a post (from several years ago!!) showing problems with antivirus software causing blue screens on certain .sys files, so I thought, what the hell, I’ll uninstall Avast. My system’s been running beautifully since then ;-P (and that’s with the wireless networking enabled again).
So, clearly it’s an issue with both of these things in combination. Remove one of them, and Windows 7 works great. By the way, I am really impressed with W7 so far – it’s a GREAT step forward from Vista.
Thanks for your post, and I hope other people find it useful too.
January 28th, 2010
Avast 5 causing bsod on my high performance machine with vista running on it, even to the point of making safe mode partially unable to work, which truly surprising me. Repeated bsod’s, uninstalled avast5, installed avira, problem solved. I am pretty depressed as avast has been my program on 3 machines for years and years, and what I have suggested to MANY others, even setup on many people machines when they needed help. After the mistake a couple of months ago on their virus defs, which caused a meltdown with many programs, leaving me having to reinstall them and take much time straightening them out, I think I have HAD IT with avast, once and for all. Saddening though.