Remote locks but doesn't unlock
 

I'm not sure why but my key remote stopped unlocking the door recently, but it still locks remotely. When I attempt to unlock the lights come on as they usually do, but the door doesn't unlock. I can manually unlock the doors, but not with the remote. Any ideas what's going on? Any help is appreciated.

Are you able to lock and unlock the car from the unit inside the car? Have you tested the battery on your key? Start ruling out some of these relating issues.

Might try searching in the tech articles to see if you find something relating to your particular issue:BMW Technical Articles - E30 E36 E46 E90 E60 E39 Z3 - Pelican Parts

Everything works as it should i.e. I can lock and unlock the door manually with the center console button. I can lock and unlock manually with the key in the door. It just won't unlock with the key remote, but it will lock. I changed the key battery about a year ago, and everything was working fine until about two weeks ago when it stopped unlocking. Can't figure out why . . yet.

First of all: which 5 series model and built year? E34? And is it a original BMW remote control or aftermarket?
In case it is a E34, here are the wiring diagrams by built year
E34 (1988 to 1995 5 Series) Wiring Diagrams