Can connect to remote iMac but can't control

I recently installed TeamViewer 13 on an iMac running High Sierra. I set it up for unattended access. From my MacBook Air with High Sierra I can connect to the iMac, and see the login screen but am blocked from clicking on anything or typing in a password. Yesyerday when I had the same experience, except later in the day I was able to activate. Any suggestions as to what I may be doing wrong?

Thanks
Gary