When a test fails due to an exception thrown in a coded step, you need to see the code to diagnose the failure. For example:
System.NullReferenceException: Object reference not set to an instance of an object.
   at FT_GOPI_IndividualRegistrationStage1_v1.Data_Entry_TIN_Registration.Data_Entry_TIN_Registration_CodedStep() in c:\Users\UAT 11\Documents\Test Studio Projects\FT-GOPI-OnlineRegistration-v1\Offline Registration\Data Entry TIN Registration.tstest.cs:line 98

The problem is that when you click Export in the Step Failure Details dialog, the code is not included. It would be useful to include the code for a failed coded step, either the code for just that step, or the entire code behind file for the test (or subtest) that was running at the point of failure.