Hello !
This ismy second post on this topic. The first one do not appear. Maybe I make a mistake.
An older program versioncan not open files create in a newer version. This is available for all programs, not only for SW.
SW, like all other programs, can run files create in older versions but, if you modify something, you can save ONLY in the current version, unlike other programs wich can save files in older versions. This is the sailpolicy of SW team.
Try to save your files in other formats. Use SAVE AS command and choose IGES or PARASOLID or other format maybe SW 2007 can read one of this. Is only an idea, I do not know if that work.
Good luck !