Windows paths may contain a colon (:) as a part of drive designation and backslashes (example c:\, g:\). However, in rsync syntax, a colon in a path means searching for a remote host.
Solution: use absolute path 'a la unix', replace backslashes (\) with slashes (/) and put -/cygdrive/- in front of the drive letter.
Example :
C:\WORK\* --> /cygdrive/c/work/*