If you run a specific test from this customers project the browser launches (but does not even try to navigate) and you immediately get:
'8/15/2013 11:26:26 AM' - System.ArgumentException: An item with the same key has already been added.
   at System.ThrowHelper.ThrowArgumentException(ExceptionResource resource)
   at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add)
   at ArtOfTest.WebAii.Design.Execution.StepsTracer.RecurseBranches(LogicalBranchData bd, Int32& orderCounter)
   at ArtOfTest.WebAii.Design.Execution.StepsTracer.RecurseBranches(LogicalBranchData bd, Int32& orderCounter)
   at ArtOfTest.WebAii.Design.Execution.StepsTracer.Trace(Test test)
   at ArtOfTest.WebAii.Design.Execution.StepsTracer..ctor(Test test)
   at ArtOfTest.WebAii.Design.Execution.ExecutionEngine.InternalExecuteSteps(AutomationStepList stepList, TestResult testResult, Object codeBehindInstance, Boolean& stopExecution)
   at ArtOfTest.WebAii.Design.Execution.ExecutionEngine.InternalExecuteTestIteration(Object codeBehindInstance, Boolean isDataDriven)
   at ArtOfTest.WebAii.Design.Execution.ExecutionEngine.InternalExecuteTest(Test test, TestResult initializationResult)
   at ArtOfTest.WebAii.Design.Execution.TestExecuteProxy.ExecuteTest(ExecuteTestCommand command)