after destroying mercer frey, I picked up the eyes of falmer from his body and no objective listed under miscellaneous to deliver eyes to Delvin. The guide mentions that Eye of Falmer(second gem) can be found on Mercer Frey's corpse. Well, I have tried everything I can think of even deposting eyes in Delvin's pocket and nothing works. Any ideas?

I know there are two eyes of Falmer, did you pick up both? If not you might have picked up the wrong one, only one eye of Falmer can be given to Devin (The Left Eye of Falmer to be specific)