I found this online on
Ramforum.com
".....OK i had this exact same problem, its an easy Fix. Disconnect your battery completely. After its disconnect, take the two Leads, positive and Negative and touch those two cables together. Be sure they are not hooked to battery! What this does is reset your computer in your truck. Then it will recognize the key fob. This happened to me when i got my truck detailed a few weeks ago and the kids cleaning it, had the music going, head lights on and wipers on with the truck shut off. They ran my battery completely down. Thats when i had this problem trying to get it started back. Took me almost 3 hours to figure it out. When i finally did figure it out, it was one of those, (cant hurt nothing now) moments. And it actually works..."