Debugging a parallel code may be difficult, but you should at least verify if your problem is reproducible on different architectures/software configurations/input data sets, and if there is some particular condition that activates the bug. If this doesn't seem to happen, the odds are that the problem is not in QUANTUM ESPRESSO. You may still report your problem, but consider that reports like "it crashes with...(obscure MPI error)" contain 0 bits of information and are likely to get 0 bits of answers.
Concerning MPI libraries in particular, useful information can be
found in Axel's web site:
http://www.theochem.rub.de/ axel.kohlmeyer/cpmd-linux.html, and in the
following message by Javier Antonio Montoya:
http://www.democritos.it/pipermail/pw_forum/2008-April/008818.html