Is this reliable enough now that it happens every time on this machine? i.e., freezing on the blue screen when the second DirectRT session is called? If so, could you post a simplified zipped version of the experiment--i.e., simplified in the sense that it's a copy but reduced down to the minimal content required to reproduce the error? I'll take a look and see if I can figure out what could be up. You could also try this yourself--i.e., make a copy of the experiment and in that copy--eliminate everything except for the que that calls the two DirectRT files. Then run that que on its own, perhaps even eliminating all but a few questions that precede and follow the DirectRT components. See if you get the same result. If so, please let me know. If not, then you can gradually add the components you took away and try to find the point at which the problem recurs.