The path for the inserted file which is passed to my mail program is built with this calculation:

SeedCode_TrimReturn ( LeftValues ( Mailing::z_MailingAttachmentTempGlob ; 1 ))

Which returns the first value. The stored reference is the following two values:
file:frictionless.xml
filemac:/2GhzDuoMac HD/all Documents/to do/frictionless.xml

So it seems like the path should be the second item not the first item to make this work.

Changing to RightValues makes it work for me.