TMK

So I replaced the TPM sensors in my 2008 M5 as I kept getting the "malfunction" message (with the orange wheel indicator). It seemed okay for about a day, no indicators, but now I'm getting a "tire low" message instead...this also goes away if I reset the TPM system, but then will come back after a while. I've checked the tires and the pressure is fine...any idea on what's going on? Do I need to replace another part?