TypeMock with Concurrent Builds

Can anyone provide some advice on how to run TypeMock in concurrent builds. We are seeing sporadic failures that I suspect come from multiple concurrent builds registering/unregistering typemock using the NAnt task.

For example:
Project 1 Register |--------------| Unregister

Project 2 --------- Register |----x failure

Looking at the NAnt output, register succeeds, but unregister fails with the following message:
[echo] Stopping TypeMock...
[typemockstop] Error undeploying TypeMock.NET TypeMock.NET was not deployed using Auto Deploy
[echo] TypeMock stopped.

Also, the failing tests had the following message:
[exec] *** You are running a 64 bit application with TypeMock.NET 32 bit.
[exec] Please install TypeMock.NET x64.
[exec] Note: .NET 2.0 applications will by default run on 64 bit
[exec] at TypeMock.MockManager.Init(Boolean collectAllCalls)
[exec] at TypeMock.MockManager.Init()

Any help would be appreciated.

- Michael