You need to open the Java Control Panel (in Start Menu → Control Panel)

Then switch to the Security tab, and (near the bottom) “Edit Site List”.

Add a new site of “https://imagenow.umn.edu/webnow/”, then hit OK a few times to close the control panel.

Now WebNow should load, if you go to its site: https://imagenow.umn.edu/webnow/

It does still pop up a security confirmation box where you have to check a box to proceed, but you should then get the login page.