Hello Ravi,
the following bug seems to apply:
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CSCsb97700 Bug Details
Assert failure in ../src-l2-les-common/stp_les_shim.c line 1340
First Found-in Version 12.0(5)WC11
Upon certain load when multivlan ports are used switch might start logging assert failures in line 1340.
Work-around: if possible avoid using multivlan ports (yet needs to be related).
Further information:
This problem has been seen when a Topology Change Notice is recevied on a Multivlan port
carrying a large number of vlans and more then one Multivlan port is present on the switch
The traceback does not seem to indicate any problem with the operation of the switch
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The bug seems to have no operational impact...
HTH,
GP