Full Answer: CRC errors

Cisco networking CRC errors are generally at layer 1 issue caused by a 
faulty port on the device or bad Ethernet cable. Changing the cable or 
swapping the port is a relatively easy fix. 

<> Occasionally they are generated on layer 2 by a duplex mismatch. 
   This happens when the port on one device is set for full-duplex 
   and the port on the connected peer device is set for 
   half-duplex. The ports can be compared by using the show interface 
   command on both devices, to see speed and duplex.

<> In TDM networks, there are many problems that cause CRC errors. 
   They include faulty wiring or cross-connects, bad repeater cards, 
   flakey smart jacks, or bad cable and channel cards. Isolating the 
   cause of these errors usually requires the telecommunications provider 
   to conduct loopback testing or to dispatch a field engineer to the 
   site to test head-to-head with the central office.

<> Personal computers receive CRC error messages when they are reading 
   files and detect corrupt data. Bad hard drive sectors, scratched or 
   dirty external media, loose wiring inside the computer and faulty 
   external drives or buggy software are all potential causes. Troubleshooting 
   procedures to isolate the cause of the errors include cleaning the DVD, 
   reloading or updating software programs, performing hardware diagnostic 
   tests and possibly replacing external drives.