Here are some of the common causes we have seen:
1)Faulty/loose cross connects at the local telco
2)Channel card failure at the local telco
3)Bad/wet splices in the transmission cable between the telco and demark
4)Cable damage between the telco and the demark
5)Bad repeaters between the telco and the demark
6)Configuration errors for that channel in the main frame switch
7)Loose/poor cabling between the demark and smart jack, or between the smart jack and the CSU/DSU
8)Horizontal cable run between the demark and smart jack, or between the smart jack and CSU/DSU run too close to power cables or fluorescent lights
9)Bad smart jack at the location
If you just started experiencing these errors, I would likely rule out items 7 and 8.
Our biggest problems come from items 4 and 5. Physical problems between the telco and demark should be easily identifiable by the frame relay service provider by looping up the smart jack and running test patterns.
We also have had some problems caused by misconfigurations in the main frame switch. A tech from our frame service provider accidentally misconfigured one of our channels when provisdioning a connection for another customer. It took allot of troubleshooting to get the frame relay group to admit they had a problem. When they ran test patterns to the smart jack, it ran clean because they were testing to the configured channel’s settings, not what it was supposed to be set to.