ML320 Remote Key Not Working
 

My wife's 2001 ML320's key remote won't work. The following is a list of troubleshooting steps I've already tried and what I encountered:

1. I changed the batteries in the remote (They're also installed correctly).
2. I synched the remote multiple times using the instructions in the owners manual.
3. Synching the remote allowed the remote to work one time only to either lock, or unlock the doors.
4. I checked the fuse and it looked fine.
5. The doors are able to be locked/unlocked by the switch near the window controls inside the vehicle.

I was hoping someone could point me in the right direction on what might be wrong, or if I should go ahead and send it in the shop. Thanks