Samba copy some files fail "invalid argument"

I am copying a directory full of files from one Ubuntu machine to another using Samba an Nautilus. Most of the files seem to be OK but some are failing to copy and I can see no patte of why. The error message is "invalid argument".

I don't think it is relevant but the files are going to an exteal USB coected hard disk on the target machine.

How to I fix this?

Added after original posting. It has gone further now and seems to be rejecting everything with the same error.