In that tweet it says that you are running it on Galaxy S2, but here it was mentioned that it is a HD2 (in the original post). Which one of them is it?
HD2 is not officially compatible with Viber, and this may be the source of the problem.
If you are seeing this problem on a Galaxy S2 (it keeps asking you to update, even though you have the latest version), then this is a problem, and we kindly ask that you take a minute and report the details of the problem to our support team using this direct link: http://bit.ly/ukGVJ0
(when you submit the ticket, please make sure to add the URL of our conversation). With this information, our development team will hopefully be able to find the source of the problem, and ultimately resolve it.
Thanks in advance