Comment 15 for bug 659854

Same thing on x86_64 ever since 10.10 update. Switched to "Nautilus Elementary" - but same issue, so it is likely some underlying service Nautilus uses (samba?) changed api/command line args, and thus the "invalid argument" error.

If this helps, there is no issue copying files from command line (via ~/.gvfs), only through Nautilus. Another little note of interest - it DOES copy first 10k -64k bytes before crapping out, but it is not consistent as same file may be 12k on one try and 30k on another and 64k on third