Using Ditto across a windows network
You have to use proper capitalization because paths in arguments are case-sensitive and I'm not sure if the double quotes are set properly to escape the blank. So try instead:

ditto -V smb://10.XXX.XXX.XXX/C/Users/john.smithy/Documents /Volumes/Macintosh\ HD/Users/john.smithy/Documents


or

ditto -V smb://10.XXX.XXX.XXX/C/Users/john.smithy/Documents "/Volumes/Macintosh HD/Users/john.smithy/Documents"


This doesn't apply if one or both of the "Documents" folder really have the name "documents". At least the standard OS X volumes and users folder have the names Volumes and Users!