Core issue
Devices connected to a Catalyst 4000 switch may experience partial or full loss of network connectivity. The loss of connectivity may affect only a portion of the switch ports and may include the uplink ports. The problem is due to an SRAM component failure which is transient in nature.
These symptoms are accompanied by rapidly increasing invalid CRC packets within the switch which can be viewed by issuing the command show nvramenv 1. If a small number of InvalidPacketBufferCrcs are seen and the number is not increasing, then that is not an indication of the problem.
Resolution
For a workaround, hard reset the switch by powering it off and on.
For more information about this issue, refer to these Cisco bug ID's:
For further assistance and support, open a case with Cisco Technical Support.