Thanks for that simplified procedure... it works for me. That is somewhat easier when doing a bunch of editing than manual conversions of gdb to gpx. I too have had the Mapsource crash when trying to save to gpx since upgrading to 6.15.6. I sent them an error report on the website and got this for a response:
Thank you for contacting Garmin Cartography. This is a known issue and should be fixed in a future MapSource update. I apologize for the hassles.
Please let me know if you have any other questions and thank you for your interest in Garmin.
Regards,
Nathan