Hi dlago,
in the SDK 5 under the libs path you will find a TTNCom.dll.
This is (somewhere deep in the SDK documentation noted) the "compatiblity" dll.
Such DLLs are imaginable as things with two ends.
One end is your app (SDK calls) and the other is the navigator.
This DLL is SDK 3 on the frontend - and on the backend it talks to Navitator 5.
Take care - only the functions provided in SDK 5 are available with this dll.
This means - you can call everthing - for an example Itinerary functions which are not available in SDK 5.
The result of such call is not documented!!!
To use it - simply replace the TTNCom.dll in your project with the one from SDK 5.
Regards
Manfred