I find I have to use Bethany's arm all the time this summer rather than her butt for the sensor insertion. I was told by Medtronic that it could be sweat that interferes with the connection of the transmitter. I am posting to see if this happens with other Medtronic CGM users? I dont remember this happening to such extremes last summer. We are getting our Dexcom tomorrow and I am praying I don't run into the same problem.