(I don't know what happened to the previous post--I may have deleted it, my apologies.)

The problem is the ":" in the path name, which the Finder sees as a directory delimiter. Try using POSIX path of filepath.

...

BTW: I really like your syntax:

get first source whose kind is audio CD

And therefore, for example:

get name of every playlist of (source 1 whose kind is iPod)

This makes me feel good, too:

get name of every playlist of (some source whose kind is iPod)

Neat!