Inside of the foundation folder there should be a file named _functions. The underscore in front of the name indicates that it's a partial file and is compiled into app.css using @import.
1: Check to see if _functions is in the foundation folder
2: If it is, check your import path
3: If it's not, try downloading Foundation again
Just as a tip, I like to use a app called Mixture.io. In addition to having a lots of its own features, it makes setting up a Foundation project a cinch.
Hope this helps.