Kitchen Aid Model KBLC36MHS01

I continually have a problem with ice formation at the bottom of my freezer.  There has been as much as 1 inch of ice in the bottom left back corner which causes me to shut off the unit for at least 24 hours. I cannot open the door of the freezer when this happens.  I have been away from the home for the past 2 months and alas there is 1/2 inch ice build up again.  The only thing I do is to turn off the freezer for 24 hours to let everything thaw.  This was a new refrigerator when I purchased this home in 2001 and it is a continual problem. I also have a Sub Zero like this one in my other home and have the same problem.  It is like the water line freezes and then it puddles and forms ice at the bottom.  Is this a common problem with this refrigerator and what is the fix?  HELP PLEASE!