accessing smbfs volume using nautilus

I've got a new install of FreeBSD 5.1-RELEASE, and have installed gnome 2.2.1.
Using Nautilus I access a volume mounted using smbfs.  The files display
correctly, but I get loads of messages:

smb_maperror: Unmapped error 1:158

on the console, and accessing the files seems very slow.   
Is this a bug, or am I missing some mount_smbfs option?

--
Bruce Cran