getsockopt failed strangely: Invalid argument

Can anybody explain what's going on? My (otherwise normal-behaving) workstation spits out the following:

$ uname -a
Linux myhostname 2.6.18.5-gg10-mixed64-32 #1 SMP Tue May 8 22:29:42
PDT 2007 x86_64 GNU/Linux

$ sudo iptables -L
Chain INPUT (policy ACCEPT)
target     prot opt source               destination
getsockopt failed strangely: Invalid argument
ACCEPT     tcp  --  anywhere             anywhere

Please let me know what other information, if any, would be useful.

Thanks in advance,

Yang