multicast group memberships exceeded in FreeBSD 6-Prerelease

[Nik]

OSPF: can't setsockopt IP_ADD_MEMBERSHIP (fd 6, addr 192.56.14.22 <
http://192.56.14.22>, ifindex 31, AllSPFRouters):
Address already in use;perhaps a kernel limit on # of multicast group
memberships has been exceeded?

I'm having this problem in FreeBSD 6-Prerelease. I think this problem has
been solved since I'm having this problem in FreeBSD 5-stable. Can anyone
help me in solving this problem. If there is any patch, can you provid me
the way to patch cause I'm never do any of patching before.

Thanks.