Cisco 12000 series routers and IOS XR.

Is anyone on the list running the Cisco 12000 Series routers with XR? We have a couple of these in our network and are having a few issues with them. Specifically the line cards will reboot for some unknown reason (12000-SIP-501). We recently replaced one of the cards and the new hardware (<6mo old) is doing the same thing. Anyone have issues with these routers? -- Jim Wininger