I had a similar problem with nfs after enabling packet queueing (CBQ) on the interface. I've since disabled queueing on the internal interface as an interim solution, but am planning on installing an additional NIC for nfs stuff.
I experienced the nfsd send error 55 with a linux client too. btw, $ grep 55 /usr/src/sys/sys/errno.h #define ENOBUFS 55 /* No buffer space available */ Graham
