System.InvalidProgramException when testing web service

I'm getting the following exception when running type mock:

System.InvalidProgramException: Common Language Runtime detected an invalid program..

stack trace is this:

at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializerContract..ctor()
--- End of inner exception stack trace ---
at System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean noCheck, Boolean& canBeCached, RuntimeMethodHandle& ctor, Boolean& bNeedSecurityCheck)
at System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean fillCache)
at System.RuntimeType.CreateInstanceImpl(Boolean publicOnly, Boolean skipVisibilityChecks, Boolean fillCache)
at System.Activator.CreateInstance(Type type, Boolean nonPublic)
at System.Activator.CreateInstance(Type type)
at System.Xml.Serialization.TempAssembly.get_Contract()
at System.Xml.Serialization.XmlSerializer.FromMappings(XmlMapping[] mappings, Type type)
at System.Web.Services.Protocols.SoapClientType..ctor(Type type)
at System.Web.Services.Protocols.SoapHttpClientProtocol..ctor()
at Connect.Sdk.SoapServiceClient..ctor(String url) in C:workConnectGateway.0SolutionsMainConnect.SdkSoapServiceClient.cs:line 25
at Connect.Sdk.ClientServiceFactory.GetService(ServiceTransport transport) in C:workConnectGateway.0SolutionsMainConnect.SdkClientServiceFactory.cs:line 33
at Connect.Sdk.ConnectMessage.Invoke() in C:workConnectGateway.0SolutionsMainConnect.SdkConnectMessage.cs:line 128
at Connect.Sdk.Manager.EntityManager`2.InvokeMessage(Request request) in C:workConnectGateway.0SolutionsMainConnect.SdkManagerEntityManager.cs:line 105
at Connect.Sdk.Manager.PipelineOriginationManager.List(Int32 clientId) in C:workConnectGateway.0SolutionsMainConnect.SdkManagerPipelineOriginationManager.cs:line 60
at Connect.Rules.Test.PipelineOriginationValidationRuleSetTest.Class_Initialize(TestContext context) in C:workConnectGateway.0SolutionsMainTestConnect.Rules.TestPipelineOriginationValidationRuleSetTest.cs:line 46


The test project in which the test sits does not use any type mock features but the exception disappears when I disable TypeMock. I'm using v 3.5.1 of TypeMock.

Any ideas?