FluentBooks is not compatible with Live Authentication over Azure ACS. To work around this issue, you need to create the Web Application extension with Windows authentication.
1. Open Central Administration and go to “Manage web applications”
2. Select a web application where PWA is located and then click “Extend”
4. After it is done, open your PWA in a newly created extension like http://<server>:8080/<pwa> and select your Live ID authentication
5. Add a new user account to PWA site for your domain account in format DOMAIN\account, and make sure it is Active Directory account
6. Close your browser (also may require log off from PC) and open again with URL http://<server>:8080/<pwa> , select “Windows Authentication” and log in use your windows credentials to make sure you assign permissions correct (prefix must be i:0#.w)
7. If you are does NOT able to login, please go to step #4 and verify permissions granted for windows account
8. Then return to the Central Administration → Manage web applications, Select a web application where PWA is located and then click “Authentication Providers” and then click on the name of the extended zone provided in step #3
9. Uncheck “Trusted Identity provider” to leave only windows authentication for this extension and save changes:
10. Open your PWA (http://<server>:8080/<pwa>) again and make sure you are able to authenticate using windows credentials.