There was a pretty long thread on this a while back. Basically there were some quality issues with the fob system on a few (not a lot) of the XLRs. There were also some issues with using the fob at a Speedpass-type place.
To see if your system is working properly is a bit time consuming. Basically take the fob out of your pocket, put the fob on top of the center console and start the engine (in park, of course). Open and close the drivers door (I know this sounds silly) and watch the driver information center display. You should get no error messages (Fob Not Found, specifically). Try opening and closing (with a slight delay after closing) the door about 10 times. If you get no error messages, then this is a good thing.
Now, move the fob to the driver's lap and repeat. Then try a few different driver locations (hand, pocket, etc). Each time repeating about 10 (or more) times. If the system is working right you maybe should get one error message. If you get more than that, check your battery. If the battery is OK and you are getting error messages at multiple locations and while the XLR is parked at different places, then it is time to see your dealer. You may have to convince the dealer. I did that by making a map of the percentages of failure at different locations within the XLR.
The solution for my XLR was to replace the control module for the keyless system. This is an 8 hour job (I kid you not). Since that time I get (at most) 1 error message in a month. 99% of the time the system works perfectly.