I've downloaded xgraph-12.1 sources and just checked with xCode that problem was in alloc.c. Functions do not work properly on Mac SL 10.6.5 (for example, Calloc does not allocate enough memory). So, I 've just replaced all calls of custom functions declared in alloc.c with system ones. And now it is working! :)
-- Regards, Eugene Dudnyk.
