Test shell runner error: object reference not set to an instance of an object

When i am running any test case from Test shell runner i am getting the error "object reference not set to an instance of an object". But when running from Test shell studio i dont face this issue. can any one help what could be the issue here and how to solve it?

Additional details:

Object reference not set to an instance of an object. (QualiSystems.TestShell.Runtime.Plugin) ------------------------------ Program Location: at QualiSystems.TestShell.Runtime.Logic.RunningTestHelper.GetStackTrace(IScriptContext context) at QualiSystems.TestShell.CanvasDocument.RuntimePlugin.ErrorObserver.CreateRuntimeTestError(Step step, IIdentifiedInfo runningObject, Int32 branchIndex, RuntimeError runtimeError, String message) at QualiSystems.TestShell.CanvasDocument.RuntimePlugin.ErrorObserver.OnScriptTaskError(Object sender, ErrorEventArgs e) at System.EventHandler`1.Invoke(Object sender, TEventArgs e) at QualiSystems.Infrastructure.ScriptEngine.Scripts.ScriptTaskBase.OnError(Exception e) at QualiSystems.Infrastructure.ScriptEngine.Scripts.ScriptTaskBase.HandleError(Exception ex) at QualiSystems.Infrastructure.ScriptEngine.Scripts.ScriptTaskBase.a(Action`1 A_0) at QualiSystems.Infrastructure.ScriptEngine.Scripts.ScriptTaskBase.HandleScriptStarted(IScriptContext scriptContext, IScriptTask scriptTask) at QualiSystems.Infrastructure.ScriptEngine.Scripts.ScriptTask.Run() at QualiSystems.Infrastructure.ScriptEngine.Scripts.ThreadPool.a(Object A_0) at System.Threading.ThreadHelper.ThreadStart_Context(Object state) at System.Threading.ExecutionContext.runTryCode(Object userData) at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData) at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Threading.ThreadHelper.ThreadStart(Object obj)