Hi Jose,
Good that you have solved, here are a few general hints (that might help others with the same problem):
Bumpy does not work on GMax code (you can decompile it to SCASM, but Bumpy will not recognise it). So only FSSC, AFW, GroundMaker code works. So if you have made aprons in GMax you will have to find other ways to make them smooth.
If you are making the grass smooth as well, you have basically lost the reason to use Bumpy. In that case it is probably more efficient to just draw a simple SurfaceType rectangle in a tool like AFW, instead of checking for the shapes of each taxiway (as Bumpy does). That only makes sense if you are trying to keep the grass bumpy.