Running tests under MSTest on TeamCity never launches the app

We are attempting to run WPF tests via TestStudio under TeamCity.  I have been trying to avoid using a hard coded WPF application path, as we are letting TeamCity checkout the source code to a temp directory.  I set up an environment variable the tests to use an environment variable to locate the application but we running under TeamCity's MSTest to be %env.teamcity.build.checkoutDir%\project\bin\Release\project.exe.  While using the VS TestStudio plug-in the application loads however, when running on TeamCity it is never able to locate the application.

[16:53:13][Step 2/4] MSTest

[16:53:14][MSTest] Found 4 test definitions.

[16:53:14][MSTest] clickbutton

[16:53:14][clickbutton] ------------------------------------------------------------ '11/14/2013 4:52:14 PM' - Using .Net Runtime version: '4.0.30319.17929' for test execution. Build version is '2013.1.1114.0'. '11/14/2013 4:52:14 PM' - Starting execution.... '11/14/2013 4:52:18 PM' - Failure detected during execution. Details: ------------------------------------------------------------ '11/14/2013 4:52:18 PM' - System.IO.FileNotFoundException: Could not load file or assembly 'file:///C:\TeamCity\buildAgent\temp\buildTmp\testuser_VM-UNITTEST 2013-11-14 16_52_01\Out\%env.teamcity.build.checkoutDir%\project\bin\Release\project.exe' or one of its dependencies. The system cannot find the file specified. File name: 'file:///C:\TeamCity\buildAgent\temp\buildTmp\testuser_VM-UNITTEST 2013-11-14 16_52_01\Out\%env.teamcity.build.checkoutDir%\project\bin\Release\project.exe' at System.Reflection.RuntimeAssembly._nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, RuntimeAssembly locationHint, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks) at System.Reflection.RuntimeAssembly.nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, RuntimeAssembly locationHint, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks) at System.Reflection.RuntimeAssembly.InternalLoadAssemblyName(AssemblyName assemblyRef, Evidence assemblySecurity, RuntimeAssembly reqAssembly, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks) at System.Reflection.RuntimeAssembly.InternalLoadAssemblyName(AssemblyName assemblyRef, Evidence assemblySecurity, RuntimeAssembly reqAssembly, StackCrawlMark& stackMark, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks) at System.Reflection.RuntimeAssembly.InternalLoadFrom(String assemblyFile, Evidence securityEvidence, Byte[] hashValue, AssemblyHashAlgorithm hashAlgorithm, Boolean forIntrospection, Boolean suppressSecurityChecks, StackCrawlMark& stackMark) at System.Reflection.Assembly.ReflectionOnlyLoadFrom(String assemblyFile) at ArtOfTest.WebAii.Design.Execution.ExecutionEngine.ValidateApplication(String file) at ArtOfTest.WebAii.Design.Execution.ExecutionEngine.InitializeWpf(ExecutionEngineCreateParams initParams) at ArtOfTest.WebAii.Design.Execution.TestExecuteProxy.CreateAndInitializeEngine(Test test, ExecutionEngineCreateParams cp) at ArtOfTest.WebAii.Design.Execution.TestExecuteProxy.ExecuteTest(ExecuteTestCommand command) WRN: Assembly binding logging is turned OFF. To enable assembly bind failure logging, set the registry value [HKLM\Software\Microsoft\Fusion!EnableLog] (DWORD) to 1. Note: There is some performance penalty associated with assembly bind failure logging. To turn this feature off, remove the registry value [HKLM\Software\Microsoft\Fusion!EnableLog]. ------------------------------------------------------------ '11/14/2013 4:52:19 PM' - Test completed!