Harry is not a professional FORTRAN programmer. The forrtl: error (75): floating point exception usually division by zero or overflow. In this case, it is probably an overflow, hence the large negative number in OpTotSq. In the early days some computers had 16 or 32 bit registers only. The leftmost bit was reserved for sign bit to indicate positive or negative number. However, if a number was defined as an Integer and was too large , eg. for a 16 bit register larger than 65536, the leftmost bit of 0 (positive number) was changed to 1 ( negative number ) hence the large negative result.
This is FORTRAN 101. Harry must have been a scientist-turned-programmer without a proper training.
Of course, I would have to see the code to be 100%, but most probably that is what happened. The OpTotSq should have been defined as a floating point number and not as an Integer. That is why it worked before, the number was less than for example 65536 for 16 bit machine. Once over 65536, it became negative.
