You likely have an old version in a directory listed in your path before C:\Windows\System32\ which is where robocopy is normally located. To find out where your copy is running from run where robocopy. On a regular system the result would be:
C:\>where robocopyC:\Windows\System32\Robocopy.exeC:\Program Files (x86)\Windows Resource Kits\Tools\robocopy.exeC:\>