Not creating Test instances into Test Lab

Hello

I am using HP ALM 11.52 and

I am creating many Tests in a loop and create a testset for that and try it to put into Test Plan and Test Lab. 

Adding into Testplan is not a problem, it's working fine, but i have problems in adding into Testlab. It's not creating for every request a Testinstance.

Here is a sample code how i get a test, create a testinstance for that and trying to create a run for that instance with the status passed.

Test testInstance = QC.GetTest(testName);
TSTestFactory factory = (TSTestFactory)testset.TSTestFactory;
TSTest retVal = (TSTest)factory.AddItem(testInstance.ID);
retVal.Status = "Passed";
retVal.Post();

RunFactory runFactory = (RunFactory)retVal.RunFactory;
Run run = (Run)runFactory.AddItem("TESTNAME");          
run.Status = "Passed";
run.Post();