smbumount: You are not allowed to umount

["Robert C. Mosher II" <mosher@andrews.edu>]

I am using smbmount to mount a share:
	$ smbmount //samba/share share -o username=user
	679: session request to SAMBA failed (Called name not present)
	Password:

This works, despite whatever that error message is:
	$ mount
	...
	//samba/share on /home/user/share type smbfs (0)

But when I try to unmount it:
	$ smbumount share
	You are not allowed to umount /home/user/share

I think I should be able to unmount this mount as a normal user since
smbumount is setuid root:
	$ ls -l /usr/bin/smbumount
	-rwsr-xr-x    1 root     root       530156 Apr  7 04:03
/usr/bin/smbumount

I appear to have this exact same setup on another machine of mine, and
smbumount works fine. I don't think it should make a difference, but the
machine it works on is an i386, and this one is a sparc. Any ideas?

Thanks,
Rob Mosher