Tire Pressure Monitor Goes "Inactive" for no reason
 

I just bought my first Mini, a 2008 S with 55K mi. I've been driving it for 2 k miles and about 8 days ago my TPMS went "inactive" while driving, I checked all my tire pressures, and they were all 38PSI so I reset the TPMS and all was well for about 4 days then it came back on again, checked tires, reset TPMS and it was good for a day. Now it has been going inactive every day I reset but keeps going inactive after 20-30 miles. Does anyone have a similar experience and if so what corrected it? .