Maybe the Simwings AFCAD does not properly cancel another one?
I had this problem with Aerosoft's EDDG in the past, it was visible when looking at the airport with FSCommander, there were two sets of slightly different taxiways overlapping each other.
I don't remember the details, I think it was EDDG from the German Airports series and EDDG from VFR Germany (and only FSX's default EDDG was hidden).
Do you have other addon-scenery in this area?