It sadly isn't supposed to work that way. Sharing iTunes libraries between computers has not been a feature of iTunes. Ever. Unless you count accessing another computer's library in "viewing" mode only, where you turn on sharing on one computer and access the library from within iTunes or Frontrow on the other.
Mac user since 1987. Running Mac OS X 10.8 Mountain Lion on a MacBook Air 11" & an iMac 27" and whatever's newest for my iPhone 4s, iPad 3 and AppleTV 2.
Apple Certified System Administrator 10.6, Apple Sales Professional 2008-2011, Apple Certified Mac Technician.