Looks like it could be a bug.
CSCdy78397
Symptoms Performance may degrade and the following message may be generated for heavily utilized Fast Ethernet interfaces on a Cisco 2600 series router:
"%AMDP2_FE-3-RXOVERFLO: FastEthernet0/1 Rx FIFO Overflow".
During the time this message is displayed, performance may unexpectedly degrade even further.
Conditions This symptom is observed on a Cisco 2600 series router that is running Cisco IOS Release 12.2(11)T.
Workaround Reduce traffic on the interface until the message is no longer not displayed.
http://www.cisco.com/en/US/docs/ios/12_2t/release/notes/122tcav2.html