0:  "Involuntary switch to real mode"

     Explanation:  The computer was in protected mode but switched to
     real mode without going through DOS/16M.  This error most often occurs
     because of a stack segment exception (stack overflow), but can also
     occur if the Global Descriptor Table or Interrupt Descriptor Table is
     corrupted.

     Action:  Increase the stack size, recompile your program with stack
     overflow checking, or look into ways that the descriptor tables may have
     been overwritten.