Some users utilizing the iPhone 4S and/or iOS 5 have reported issues connecting their Instagram accounts to Twitter. Please follow these troubleshooting steps in order to fix the issue:
1. Exit Instagram and open the Settings application.
2. Locate the Twitter setting.
3. If there are any accounts listed tap to select them and then tap Delete Account from the bottom of each account’s page.
4. Open Instagram and navigate to Profile > Edit Share Settings > Twitter to connect Twitter again in Instagram.
Why us Instagram the only app on my iPhone with this “problem”?