Error Code -17400; Unable to create thread

Question

Running TestStand 4.0.  Test sequence calls many sequences that run as new executions and runs fine for up to about 8 units testing simultaneously.  After that, I get a run-time error code -17400; Unable to create thread.  There are no other details available.  The steps that generate the error are able to create the new executions initially, but eventually fail once about 22 executions are running.  I am monitoring memory resources and there does not appear to be any issues.  Any troubleshooting suggestions?  Thanks.

Answer 1

My test sequence has several test groups, each of which contain loops that create new threads (tests) for 48 UUTs.  Thus the number of running threads does get very high.  I was running into problems with Windows XP GDI Object resources once the number of threads reached about 200.  I then modified my program into smaller test groups to keep the number of threads at any time to less than 150.  GDI resources are no longer an issue, but the error -17400 unable to create thread happens after the first test group has completed and the second test group is just trying to run.  Note that the second test group runs fine if I skip the first test group, so the sequence itself should be okay.  I thought it might be a memory issue (even though there are no apparent memory issues seen in Windows Task Manager), so I set the "Unload after step executes" property for each of the new executions created.  That did not resolve the issue. 
I am trying to create a simple sequence to duplicate the error without using any of the actual test sequences that require test hardware, but have not been successful thus far.
Thanks for your replies and suggestions!