What is the reason to the fatal bounds error: Absolute pressre
 

I encountered a problem that when I stop the solver manually or let it compute to the last iteration as set, it will suggest the fatal bounds error and the variable is absolute pressure. What puzzled me is that if I stopped it at 100th steps it would suggest the error but if I stopped it at 200th steps it will suggest the error now, and it wouldn't stop at 100th step. Only when it's over it encountered the error. So what is the reason?
+--------------------------------------------------------------------+
| ERROR #001100279 has occurred in subroutine ErrAction. |
| Message: |
| Stopped in routine ENFORCE_BOUNDS |
| |
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+--------------------------------------------------------------------+
Thanks in advance!