I saw the same problem last night. My "back", "forward", and "refresh" buttons (maybe others, too) in IE8/Win7 Ultimate quit working. A reboot "fixed" the problem, at least for now.
A bit of research shows that others have seen this same problem.
I installed x32 Win7 Ultimate a week ago and there's very little installed on the PC. PrimoPDF, Steam, and Adobe Reader. That's about it. A HijackThis scan was small and clean (there's basically no third-party add-ins), as was a MalwareBytes scan and an MS Security Essentials full scan.
System Event and Application Event Logs are both very clean.
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Oh, great. I looked at my Security Event log and see this new message about the MalwareBytes program I just downloaded (and ran) from the MalwareBytes.org site:
Log Name: Security
Source: Microsoft-Windows-Security-Auditing
Date: 3/17/2010 1:30:21 PM
Event ID : 5038
Task Category: System Integrity
Level: Information
Keywords: Audit Failure
User: N/A
Computer: xxx.xxx.xxx
Description:
Code integrity determined that the image hash of a file is not valid. The file could be corrupt due to unauthorized modification or the invalid hash could indicate a potential disk device error.
File Name: \Device\HarddiskVolume2\Windows\System32\drivers\mbamswissarmy.sys
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Well, a search seems to show this Security Error is a known issue and probably nothing serious.