Can you check what error are comes on that interface?
Can you check by CABLE replacement?
Can you check proper configuration of Subnet and IP access-list associated with that interface?
If it is Module than change module and observe?
Can you check proper dumplex and speed?
Can you check arp command? how much are imcomplete entries?
If you fail or not able to judge by all test than capture traffic by sniffer and analyze that.
Regards,
DHarmesh Purohit