Ultimate Facebook plugin won't change to new Facebook user

I have UFB installed on my multisite network. Developed a FB app for site 1 http://www.olympiarealestatellp.com just fine, and set up UFB using my client's FB account which we set up for him. Now we are trying to set up client site 2 http://www.awareandvibrantliving.com. Made a new FB app for this site fine, and set UFB up using my own FB account account just fine. Now we need to switch it over to her FB account. But when I click 'Permissions and Tokens' > 'Use a new Facebook user for setup', all I get is a quick flash of a popup, and then nothing. If I log out of facebook, then try again, I get a FB login form, but I can't log in. This happens on both site 1 and site 2. Any clues to what is happening? Again, both sites set up and worked just fine the first time around, but now I can't change the FB user of either of them!