This article talks about what you can do when you see an "Unable to connect to activation service" error message on the iOS Subtext App for iPad.
When downloading purchased books on the iPad application Subtext, the user receives an error message "Unable to connect to activation service".
This issue occurs because the application sends requests with a
100-continue header, and doesn't honor the proxy's request to resend without it.
- Go to Web proxy > Web proxy > Settings.
- Click Advanced.
- Scroll down to HTTP Strict Mode, and select Disable.
- Click Save and restart.