Currently Being ModeratedRe: Even with notifications on, Viber keeps showing "notifications are off" dialog box. Reset possible?Nov 8, 2012 2:56 PM (in response to Leo Rezende)
Try testing it when connected to another Wi-Fi network, so you know your network isn't causing a problem.
Also, Apple has basic troubleshooting tips here -> iOS: Understanding Notifications
If that doesn't do it, check out Vibers support article -> Push Notifications for iPhone - How to enable
You can email them notifications test results.