[ns] error msg: Classfier::no-slot{} default handler.. (fwd)

[Yan Yu <yanyu@lecs.cs.ucla.edu>]

Hello, all,
my simulation generates this error message after it runs for some time:

--- Classfier::no-slot{} default handler (tcl/lib/ns-lib.tcl) ---
	_o31: no target for slot 0
	_o31 type: Classifier/Port
content dump:
classifier _o31
	0 offset
	0 shift
	2147483647 mask
	1 slots
		slot 255: _o33 (CMUTrace/Recv)
---------- Finished standard no-slot{} default handler ----------


ANyone has any idea what might go wrong?
Thanks a lot in advance,
yan