I found the reason of the crashes. It goes like this: you send a message to somebody who's not online, and then close the window. When the recipient goes online, it will send a delivery receipt. Yappari (since doesn't have chat history) tries to update the message (with a double checkmark) but since you closed the window the message is not found = crash.

Will be fixed in next release.

I need more people willing to test the SMS registration. So far the people that have contacted me live in countries where Whatsapp can't send SMS messages to, but they have been very helpful for fixing other bugs (thanks!!)