The official WhatsApp client for Android, iOS, Windows Phone, BlackBerry and Symbian has been recently updated. This new version includes a new security update that changes the password associated to WhatsApp accounts. Previously, the password used to be the device’s IMEI or the WiFi MAC address, but now a random generated password is used instead.
What this means? You won’t be able to use Wassapp as there is no way to know your new WhatsApp password. We are already working on this issue but it will take some time.
A temporarely solution is to use an older WhatsApp version or register another phone number from Wassapp (currently not possible, but next version will include registration support).
Sorry for the inconveniences.