Thanks for the problem solving tip KAS, we can use lots of info like that to help rule stuff out. It almost certainly has to be memory related but it can't be as simple as a quantity issue. My guess is that it is related somehow to memory management in terms of how XP and Vista differ in this regard. Will let you know if we discover anything more useful. A prize for sure for anyone who can figure this one out--or at least find a contingency that leads us to a solution. Hmm.
Note also that we are working on a version of MediaLab that is fully Vista compliant. We did DirectRT first (which is in its 10th Vista beta as of Aug 19, 2008) because it simply would not run on Vista at all. Now that it seems to be running ok we are in the alpha stages of a Vista MediaLab which should be available for user beta testing within a few months (or earlier if all goes well). Fortunately, this issue and a couple problems with playing videos seems to be all the trouble we have seen so far with MediaLab on Vista.
See also...
www.empirisoft.com/support/showthread.php?t=704