Hi Dubfault,
this is an "official" error in the TomTom Navigator.
So we can't help you in this case. As soon as TomTom ships a fixed TTN version
TTNCF as well as the SDK will work properly with negative values.
The only thing you could do is "stress" TomTom to fix this bug.
And maybe you could ask your customers also to argue about the error via mail to TomTom.
Regards
Manfred