If you have SSH'D into another router on that same ip before and then started to use the ER-PRO then yes it will show this error. if you have not then i would if i where you look into it more.
Edit the SSH known host file by doing the following.
sudo nano /Users/imac/.ssh/known_hosts
Edit the file then Control + C which will ask you are you sure you want to save the file then hit Y to save.
