When you use the OpenType font Adobe Garamond Premier Pro, discretionary ligatures might not work if the language attribute of the text is something other than US English. For example, in InDesign, using the feature in a story which has the French dictionary applied will cause the ligatures to fail. Instead of the joined glyphs, the individual glyphs will appear.
Contact Adobe Customer Service, or your software Vendor, to obtain the most recent version of the font. The issue is addressed in version 2.x of the font.