Membership Pro 2 login issue on IE

Some members who login to access our resources are within School networks and they're using Internet Explorer. (I know, I know...) Anyway, they can't get past the login prompt ( They just get a "please wait" message.
However, no issues with FireFox or Chrome.

Other than us telling our users to use a better browser, can you suggest any reason why they're having difficulty logging in? Thx!
Chris G

You're welcome to use a test user (subscriber only)
Username: member
Pass: chris