What could be reasons a WPF app would pin the CPU and lock the app on some computers but not others?

Question

Stumped here. Posted a similar question before. We have a pretty large WPF app that on some machines runs great, but on others, all of a sudden, one of the CPU cores gets pinned at 100% (just one core) and the app freezes. It usually seems to happen when showing a context menu or a combobox drop-down (i.e. Popup controls) which is why we can't debug this since no user code is executing at that time. It's driving us crazy because again, on most machines it runs fine, but on a few, it freezes.

The odd thing is when we run it in a VM, it runs great there too! Crazy! Not sure what's causing this, or more importantly, where to even begin to look because as I said, no user code is running.

This happens on only about 10% of our machines, but it consistently happens on those machines. All are clean (i.e. relatively fresh OS installs, no crazy apps, etc.) and mostly identical machines spec-wise: similar CPUs, similar RAM, same video drivers and service packs.

So as I stated in the title, can anyone suggest possible reasons why a WPF app would pin the CPU and lock the app on some computers but not others? We're just stumped!

Answer 1

Found it!! Turns out there's a bug in .NET 4.0 regarding UI Automation and the changes MS introduced. Here's the info, and the fix! (Note: Even if you call MS, they will send you a link, but it's always a broken link. I managed to track this down manually.)

Note: Their article talks about a specific case that causes this behavior, but if you google around, you'll see tons of issues around hangs related to those DLLs. The latest is they're promising a fix in the .NET 4.5 runtime (from a MS post on this issue.)

Here's the KB article...
http://support.microsoft.com/kb/2484841/en-us

...and here is the actual hotfix.
http://archive.msdn.microsoft.com/KB2484841/Release/ProjectReleases.aspx?ReleaseId=5583