On 3 machines now the Windows Store is broken. The Install and Back buttons don't work

Question

Originally reported here:  http://answers.microsoft.com/en-us/windows/forum/windows8_1-windows_store/on-3-machines-now-the-windows-store-is-broken-the/8bafdc7a-a708-4012-a4f1-b98ab8788c28
Advised to post here instead.
Hi there
On three separate Windows 8.1 Professional machines now, I've had an issue where the Store stops working properly for no apparent reason (no error messages or anything).  The store opens, and I can browse apps, and view individual apps, but
once in the app view I cannot click on the Install button or the back buttons.
They "light up" as if being pressed, but they don't actually do anything.
I've tried all the various troubleshooting, including the Windows App troubleshooter, wsreset, re-registering the store files using powershell, and renaming the cache folder in my user profile. No effect.
If I sign into the PCs as another user, then I don't get the issue. As such something is getting corrupted in the profile.
We only have around 9 or 10 Windows 8.1 PCs deployed at our organisation for testing, and three of them have had this fault, which doesn't inspire confidence. As such, we cannot progress with further deployment until we have a fix in place that
doesn't involve wiping the user profile.
Any ideas please?

Answer 1

Hi FangZhou CHEN
I've discovered the cause of this error after much searching.
Based on your suggestion, I checked the Event Viewer and found a string of "Application Error" entries similar to this:
Faulting application name: WSHost.exe, version: 6.3.9600.17093, time stamp: 0x534765e9
Faulting module name: sxwmon64.dll, version: 4.5.2608.0, time stamp: 0x52b2a853
Exception code: 0xc0000005
Fault offset: 0x00000000000257ff
Faulting process id: 0xf40
Faulting application start time: 0x01cfeeb1cc6d035e
Faulting application path: C:\WINDOWS\WinStore\WSHost.exe
Faulting module path: C:\WINDOWS\SYSTEM32\sxwmon64.dll
Report Id: 19ee9a1c-5aa5-11e4-8259-600292638f85
Faulting package full name:
Faulting package-relative application ID:
Presumably the WSHost,exe process is critical to the Store and "Metro" apps?
The offending dll file causing this process to fail, sxwmon64.dll belongs to a peice of security software on our machines called Lumension Endpoint Security (we're running version 4.5 SR2). We use this to control removable media (USB) and CDRW access for
our employees.
If I rename that particular DLL file, the store and the calendar app which I was also having issues with (it was blank), spring back into life.