I have a Verizon iPad 2 mini. This device does not have a SIM card - at least not one that can be removed/replaced. I have just begun getting an Invalid SIM message. I've tried the Airplane Mode on/off, power cycling - all the things I can find on line except, of course, removing & reinstalling the SIM. After a power cycle the message goes away & the unit works fine for about a day then get the error again & have to power cycle. Anyone got any ideas?