.Net Version Compatibility

I executed a (web) test list in which 34 of my 35 tests passed and one failed.  The failed test bombed on initial execution; I included the test log details below.  This was executed on my PC (vs. a remote/virtual machine).  I've not encountered any .Net Framework compatibility issues before.  Anyone recognize what's going on here?

Thanks in advance!

------------------------------------------------------------
'3/22/2012 1:29:17 PM' - Using .Net Runtime version: '4.0.30319.239' for tests execution.
'3/22/2012 1:29:17 PM' - Starting execution....
'3/22/2012 1:29:18 PM' - Detected custom code in test. Locating test assembly: irth_Solutions_Web_Site_Redesign.dll.
'3/22/2012 1:29:18 PM' - Failure detected during execution. Details:
------------------------------------------------------------
'3/22/2012 1:29:18 PM' - System.NotSupportedException: An attempt was made to load an assembly from a network location which would have caused the assembly to be sandboxed in previous versions of the .NET Framework. This release of the .NET Framework does not enable CAS policy by default, so this load may be dangerous. If this load is not intended to sandbox the assembly, please enable the loadFromRemoteSources switch. See http://go.microsoft.com/fwlink/?LinkId=155569 for more information.
   at System.Reflection.RuntimeAssembly.nLoadFile(String path, Evidence evidence)
   at System.Reflection.Assembly.LoadFile(String path)
   at ArtOfTest.WebAii.Design.Execution.ExecutionUtils.EnsureAssemblyExists(String assembly, String folder)
   at ArtOfTest.WebAii.Design.Execution.ExecutionUtils.CreateCodedTestInstance(Test test, TestResult result, String binariesFolder)
   at ArtOfTest.WebAii.Design.Execution.ExecutionEngine.InternalExecuteTest(Test test, TestResult initializationResult)
   at ArtOfTest.WebAii.Design.Execution.TestExecuteProxy.ExecuteTest(ExecuteTestCommand command)
------------------------------------------------------------
'3/22/2012 1:29:19 PM' - Test completed!