I've marked up a .DWG file that my draftsman has sent me and now he's telling me the that he can't open the file I've returned.

He's using Autocad 14 and can't open the file I've sent back to him no matter what he tries. He's even tried changing the extension from a .DWF back to a .DWG to no avail. In Volo View I've only got two options to choose from .... .DWF & .XML right?..

Any advice would be a real big help.

Thanks
Sheldon