Core issue
This problem occurs in switches that run Cisco IOS Software Release 12.2(18)SXF2 when Multicast is enabled. There are some instances when the created Reverse Path Forwarding (RPF) information does not get freed, for example, it causes a memory leak eventually.
This happens when you perform a RPF lookup and for some reason you do not create the mroute entry.
This problem is documented in Cisco bug ID CSCsd42121.
Resolution
In order to resolve this issue, upgrade to Cisco IOS Software Release 12.2(18)SXF4 or later, which can be downloaded from the LAN Switching Software page.
For further assistance and support, use the TAC Service Request Tool in order to open a case with Cisco Technical Support.