Ade Simple Set Problem

I installed an Accenta/Optima alarm system with the ADE Simple Set reader a couple of years ago. It has been working perfectly until a couple of months ago when for no apparent reason it "forgot" all the keyfobs associated with the simple set reader. I reprogrammed the reader to recognise the keyfobs and all was well again until today when I had the same problem of the reader not recognising any of the keyfobs. Of course as, sods law would dictate, on both occasions it was when unsetting the system that the simple set reader failed to recognise the keyfobs. I have now reprogrammed the reader and all seems well again, but I am worried that the problem may reoccur. Has anyone else experienced this problem? Or can anyone suggest why it might be occurring, and how to prevent it.

Many thanks for you help

Kenb