Nunit tests fail w/ TypeMock 5.4, TeamCity 5.2 and .Net 4.0

We have upgraded our project to .Net 4.0 and are having problems getting the Nunit tests working in TeamCity using MSBuild

We have a block of code in our MSBuild script that looks like this:

<TypeMockStart>
   <Exec  Command="path/to/nunit-console-x86.exe /path/to/Tests.dll" />
    <TypeMockStop>

This should work fine, but ever since we upgraded to .Net 4.0, I am getting this message in the logs.

Test(s) failed. TypeMock.TypeMockException :
*** Typemock Isolator is not currently enabled.
To enable do one of the following:

* To run Typemock Isolator as part of an automated process you can:
- run tests via TMockRunner.exe command line tool
- use 'TypeMockStart' tasks for MSBuild or NAnt

* To work with Typemock Isolator inside Visual Studio.NET:
set Tools->Enable Typemock Isolator from within Visual Studio

For more information consult the documentation (see 'Running' topic)
at TypeMock.MockManager.i()
at TypeMock.MockManager.Init(Boolean collectAllCalls)
at TypeMock.MockManager.h(Type A_0)
at TypeMock.MockManager.MockAll(Type type, Constructor mockConstructors)
at s.a()
at s.b()
at gv.StaticMethods[T]()
at <namespace>.<testFixture>.<testMethod>() in c:TeamCityuildAgentworkbbef895a6382114<testClass>.cs:line 114

Does TypeMockStart work when the NUnit tests are run in .Net 4.0?