Fiesta immobiliser fault help!!!!!

Hi all, 

 Am really desperate for some advice or help if anyone has come across this issue with their fiesta. In April it broke down for the first time while I was driving at low speed. When I tried to re start the engine the immobiliser light flashed and it wouldn't start. Nothing shows on diagnostics when it is in this state and disconnecting the battery makes no difference. It will then start again after around 8-12 hours although sometimes less. This has happened 12 times now in the past four months and all the garages I have taken it to don't seem to have any answers. It has stopped when I've been driving fast, slow, idling or sometimes just won't start after being parked. Usually at least a few days between breakdowns- sometimes even two weeks. The immobiliser fault code that is flashing up is code 16 which is a communication fault. Last week when it was broken down the garage it was taken to (a local dealership that sells ford) thought they had got somewhere as it came back to life when they fiddled with the ABS connection. All connections have been checked and grease applied but it has still broken down again. Thinking about replacing the transponder as next step but wondered if anyone had this problem and could shed some light please?? Very grateful for any replies at all!!

Thanks