GPX Unknown Import Error in 4.1.2

Basecamp 4.1.2 won't open most of the GPX files that previous versions used to open OK !

These include all gpx tracks from famous sites like http://www.walkhighlands.co.uk (for example http://www.walkhighlands.co.uk/fortwilliam/profiles/buachailleetivemor.gpx)
http://www.validome.org/xml/validate/ says that this gpx file is well-formed.

Please tell me what is wrong with these GPX files - or with Basecamp!

Thank you!