2006 e350 remote door locking/unlocking system only works at night or when it's very overcast. I've tried the cupping of the hands trick, pointing the remote closely at the door handle, & changed the battery. any suggestions as to what the remote door locking/unlocking system problem might be?

 

found an old post on the subject & the advice worked!
checked the fuses, found one out, one missing!!
today I have "lockage". Thanks