Have you tried adding "sudo" in front of the "mount" command? I know it runs as Root, and it should not be necessary, but I have had a similar problem in the past, and adding sudo resolved it.
Thanks bcstring but adding sudo didn't do the trick for me.
I will try the following command as a test to see if it gets me anywhere
mount_smbfs “//domain;username:password@servername/volume" /Volumes/test_mount_point