GAC installation error when autodeploying from nant/teamcity

(Updated 2011-06-23: added the complete typemockregister, -start and -stop sections)

Hi!
One of our teams are using typemock 6.0.3.0.
They are running their build on Teamcity 6.0.2 with a build agent on a windows 2008 server. The build agent runs with an account that is local admin on the machine.

Their nant build script autodeploys typemock like this:

<!-- Dynamically load TypeMock task. -->
<if test="${common.nunit.in.use-typemock}">
<loadtasks assembly="${common.nunit.in.typemock-dir}TypeMock.NAntBuild.dll" />
<typemockregister company="Company" license="License-key" autodeploy="true"/>
<typemockstart/>
</if>

<exec program="${common.nunit.in.nunit-dir}" resultproperty="common.nunit.nunit-console-output" failonerror="false" >
<arg value="${common.nunit.in.project-path}" />
<arg value='/xml:"${common.nunit.in.project.buildlogs-dir}${common.nunit.in.testlog-filename}"' />
<arg value="${common.nunit.in.optional-arguments}" if="${string::get-length(common.nunit.in.optional-arguments) > 0}" />
</exec>

<if test="${common.nunit.in.use-typemock}">
<typemockstop undeploy="true"/>
</if>


Their build log says:
[11:09:50]: [if] loadtasks
[11:09:50]: [loadtasks] Scanning assembly "TypeMock.NAntBuild" for extensions.
[11:09:50]: [if] typemockregister
[11:09:51]: [typemockregister] Typemock Isolator Auto Deployed, version 6.0.3.0
[11:09:51]: [typemockregister] Typemock Isolator Registered successfully
[11:09:51]: [common.nunit] exec (2m:05s)
[11:09:51]: [exec] NUnit version 2.5.7.10213
[11:09:51]: [exec] Copyright (C) 2002-2009 Charlie Poole.
[11:09:51]: [exec] Copyright (C) 2002-2004 James W. Newkirk, Michael C. Two, Alexei A. Vorontsov.
[11:09:51]: [exec] Copyright (C) 2000-2002 Philip Craig.
[11:09:51]: [exec] All Rights Reserved.
[11:09:51]: [exec] Runtime Environment -
[11:09:51]: [exec] OS Version: Microsoft Windows NT 6.0.6002 Service Pack 2
[11:09:51]: [exec] CLR Version: 2.0.50727.4211 ( Net 2.0 )
[11:09:51]: [exec] ProcessModel: Default DomainUsage: Single
[11:09:51]: [exec] Execution Runtime: Default
[11:09:56]: [exec] Excluded categories: Slow
[11:11:31]: [exec] ... (test related stuff)
[11:11:31]: [exec] Errors and Failures:
[11:11:31]: [exec] 1) Test Error : (testname)
[11:11:31]: [exec] TypeMock.TypeMockException :
[11:11:31]: [exec] *** Typemock Isolator needs to be linked with Coverage Tool to run, to enable do one of the following:
[11:11:31]: [exec] 1. link the Coverage tool through the Typemock Isolator Configuration
[11:11:31]: [exec] 2. run tests via TMockRunner.exe -link
[11:11:31]: [exec] 3. use TypeMockStart tasks for MSBuild or NAnt with Link
...
and then follows all the tests that fails because typemock doesn't work.

The eventlog at the teamcity 6.0 build agent windows 2008 server says:

Installation in the global assembly cache failed: D:uildagentwork25cbe3c82c8d3b2devlibTypeMock Isolator 6.0Configuration.dll
Installation in the global assembly cache failed: D:uildagentwork25cbe3c82c8d3b2devlibTypeMock Isolator 6.0TypeMock.Interceptors.dll
Installation in the global assembly cache failed: D:uildagentwork25cbe3c82c8d3b2devlibTypeMock Isolator 6.0TypeMock.dll
Removal of an assembly from the global assembly cache failed: D:uildagentwork25cbe3c82c8d3b2devlibTypeMock Isolator 6.0TypeMock.Interceptors.dll Typemock.Interceptors,Version=6.0.3.0
Removal of an assembly from the global assembly cache failed: D:uildagentwork25cbe3c82c8d3b2devlibTypeMock Isolator 6.0TypeMock.dll TypeMock,Version=6.0.3.0

Does anyone have any idea on what we have missed?

Regards, Daniel