The following are troubleshooting suggestions when:
1. Your firewall and network should explicitly allow (i.e., "whitelist") access to:
216.200.62.*
74.125.25.95  (for ajax.googleapis.com)
As of June 20, 2017, Ebook Central is now using Cloudflare CDN to provide faster access to our content and as such you should additionally whitelist their IP range(s), which can be found here https://www.cloudflare.com/ips/
2. Certain domains cannot be blocked:
*.proquest.com
ajax.googleapis.com
cdnjs.cloudflare.com
jquery.com
bootstrapcdn.com
require.min.js
3. Javascript needs to be enabled for your browser
For directions to enable Javascript for all browser types, see:
http://www.enable-javascript.com/
4. Certain ports cannot be blocked:
All of the above domains use standard ports 80 and 443
5. Make sure your Java cache isn’t full
To clear your Java cache:
Open your computer’s Control Panel
From there, open “Java”
Under “General” tab, "Temporary Internet Files”, click “Settings…”
Then click “Delete Files…”
6. Some VPNs are not compatible with Ebook Central
URL-rewriting VPNs are not compatible with Ebook Central
7. Don’t use VPN if using another form of remote authentication, such as:
proxied links
EZproxy SSO
Athens
Shibboleth
Referring URL
8. In Safari, “Private Browsing” does not work when using proxied links