TFS 2008 test causes VSTestHOST to run with 100% CPU

Hi
I'm tried to evaluate Isolator 5.1 for Sharepoint.

When I run the sample projects the VSTestHost hangs with 100% CPU.

On the same computer, the same test runs fine with NUnit.

The last entry in the log file is:
System.Runtime.InteropServices.CriticalHandle instance void Close()
Microsoft.VisualStudio.TestTools.Common.ServiceMessage instance void GetObjectData(class System.Runtime.Serialization.SerializationInfo,value class System.Runtime.Serialization.StreamingContext)