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That is odd. RelSpace15 should be stable. I am not sure what could be causing that offhand, but the first steps to something like that should be to reinstall it (preferably downloading a fresh copy, especially from a different source if possible) or try it on a different machine/OS.
Speaking of which, what are you trying to run it in? A simple test to perform is to install a virtual machine of a different OS and install it there.
I've tried installing it on various PCs and OSes (Most versions of windows except Vista). Half of the Math Phys Labs have it installed now, thanks to my 'determination'.
How often, if at all, does the program crash on you?