Domain Registration Requests

Hi there, we’re having a problem with a subset of users, it seems. SketchUp for Schools is enabled on the OU all faculty and students are in, but some people are getting the “It looks like you’re having trouble signing in. Make sure you’ve enabled pop-up windows for SketchUp, then complete sign in using the pop-up window that appears.”
We’re a pre-k to 12 school with domain ecfs.org

Thanks for any help you can provide.