Fixing My Custom TFS 2010 Activities to Run on TFS 2012

Wow, what a technologist.  A post or two a month about everything except technology.  Well today, I'm going to document one of my most recent struggles in the hope that someone will benefit.

Started off getting this error.

TF215097: An error occurred while initializing a build for build definition \<My Project Build Name> The values provided for the root activity's arguments did not satisfy the root activity's requirements:'DynamicActivity': Expected an input parameter value of type 'Microsoft.TeamFoundation.Build.Workflow.Activities.BuildSettings' for parameter named 'BuildSettings'.'DynamicActivity': Expected an input parameter value of type 'Microsoft.TeamFoundation.Build.Workflow.Activities.TestSpecList' for parameter named 'TestSpecs'.Parameter name: rootArgumentValues

Bizarre.  So what it comes down to is that 2012 does not work with artifacts either built against or referencing a component from 2010.  A 2012 build controller won't run custom build activities (which I had) that were compiled against the TFS 2010 binaries.  Further, the custom XAML files were polluted by the workflow designer, said to be a bug in the designer, but that smells fishy to me.

Here's the steps I took.

1. I rebuilt my custom activities with all the references pointing at the new 2012 TFS .dlls.  
2. I overwrote the old custom activity .dlls in the $\BuildProcessTemplates\CustomActivities directory and checked them in.
3. After that, my builds still didn't work, failing with essentially the same error, so I used the XAMLCleaner code I found here to scrub my custom build workflow templates (.XAML files).
4. Running anything and causing one of these version issues requires the build controller to be reset.  Use the TFS admin console to do so.
5. My *.CI builds all use the DefaultTemplate.xaml.  The upgrade gave me a DefaultTemplate.11.1.xaml.  I deleted the DefaultTemplate.xaml locally, renamed the DefaultTemplate.11.1.xaml to DefaultTemplate.xaml, and checked it in.  .CI builds ran fine.
6. Once I had made all these changes, I checked everything in and ran my custom web and default release builds, and they worked.

Hope this can help someone.  I love TFS ALM, but sometimes the stuff is daunting.  The two links above really helped me out.