Since my upgrade to the latest version(5.5.0 Free) of cwrsync, the keys aren't found any more.
Here is my batch that worked.
What I'm doing wrong.
REM Make environment variable changes local to this batch file
REM ** Specify where to find rsync and related files
REM Set HOME variable to your windows home directory. That makes sure
REM that ssh command creates known_hosts in a directory you have access.
REM Make cwRsync home as a part of system PATH to find required DLLs
ECHO "START RSYNC"
rsync -avzr --progress --remove-source-files '/cygdrive/e/backup/' 'firstname.lastname@example.org:/volume1/BACKUP/'