Is this actually MS-DOS, or a DOS prompt on Windows 95 or earlier, or is it the command prompt from a newer version of Windows?

Under DOS, the maximum length of a command was 128 characters, and your line is 199 characters long. If you're up against the 128 byte limit, the program is going to lose everything to the right of it (including the second quotation mark) and it will only see this:

XCOPY /C "F:Poser Runtimetextures!DREAMSQUARESDreamyRealisticEyesDRE_Black.jpg" "C:Program Filese frontierOther Runtime

which, to DOS, consists of four arguments plus the switch, which would explain the error.

There was a setting you could add to CONFIG.SYS to extend the length of the input line for COMMAND, but I'd have to look it up. I'm not sure what the restrictions (if any) are on CMD, the command interpreter that newer versions of Windows use.