Hello again gromac'ers: I don't finish yet the demo for the simple sistem. Now I run mdrun -nice 4 -s ${MOL}_pr -o ${MOL}_pr -c ${MOL}_b4md -v step 140, will finish at Fri. Oct. 3 12:05:47 2003Fatal error ci = -2147483648 should be in 0... 14078 [FILE nsgrid.c, LINE 210]. what a hell is that?. Thank you very very very much! Pablo.