Hi Jock Munro,
The problem you are talking about is known in MobiFlight.
It's the numerical value of the right single mouse click: 2,147,483,648
This numerical value is exactly 1 above the maximum range of the signed long INT range.
Binary this area goes to 0111 1111 1111 1111 1111 1111 1111 1111,
These are (+)2,147,483,647. As you can see, the MSB is 0, which is why the number is considered a positive number. If 1 is added, we have
1000 0000 0000 0000 0000 0000 0000 0000
If the sign is negative and the rest of all bits is 0. So -0. 0, mathematically speaking, can not be negative, so an error is output.
If, however, the 2.147.483.648 is preceded by a minus (-), then it is almost the smallest representable number of -2,147,483,648, so the result is -2,147,483,648, which is binary 1000 0000 0000 0000 0000 0000 0000 0000. Mobiflight can take this value.
So much for explaining why (only) this value must be negative.
Where did you actually get the EventID 69751 from? According to my documents, that is not forgiven or documented.
Please try also for the clockwise rotation (increase) the EventID 69850 and the parameter -2147483648. That should work