Sometimes this happens when the results.xml is incomplete and probably because QTP crashed. You can try opening this results file in notepad and search for status=''Failed'' to see if there are any fails. You will still need to run your test again to get the full results.

Also, check and see if you have a large number of temp result folders created. QTP does have a utility for cleaning up old result logs which is is installed Start > QTP > Tools > ''Run Results Deletion Tool''. Recommend running cleanup on the machine weekly and see if the issue goes away.