The issue is resolved in Cisco bug ID CSCdy57722 by a Cisco IOS Software upgrade.
For a workaround, perform these steps:
Disable the RTP header compression link.
Disable fast switching on the Frame Relay connection by issuing the no ip route-cache command under the interfaces.Note: This may cause the router's CPU to increase, as it now uses the process-switched path.
To resolve the problem, use a version of Cisco IOS Software that includes the fix for Cisco bug ID CSCdy57722.