We have struggled with CRC errors on routers with 2 frame relay circuits connected to a dual channel T1 card. The CRC errors seemed to only occur on the newly added secondary port on the card, and the connectivity would act intermittently. In working with Cisco, I have learned that both ports’ default clock is set to ‘line’ which gets the clocking from the ISP. When both ports are set at ‘line’, they both battle to keep up with the clocking. To fix this problem, set one of the T1 controller’s clock source to ‘internal’. This tells the port to get clocking from the other port configured as ‘line’.