Here's a quick fix for the server messages.

Also with this version there's a workaround in the registration:

1.- Install NITDroid and Official Android Whatsapp client in it.
2.- Register your N900 phone number with Whatsapp. Complete the registration up to the end.
3.- Go back to Maemo
4.- Install Yappari 0.0.18 if you haven't installed it already.
5.- Type exactly this in terminal:
6.- Start Yappari, type your N900 phone number with country code
7.- Yappari should detect the number was already registered using an Android client and log in without any problem.

Also if you are one of those users that love to go back and forth to NITDroid, if you use this method, you can switch from Yappari to NITDroid + Whatsapp and back without re-registering each time.

The deb: http://uppit.com/pmpc9xeyi4lq/yappari_0.0.18_armel.deb

Normal registration still doesn't work. I'm working on it when I can (I've been very busy at work so spare time has been almost non-existent). It's not easy to hack that. The first time was very hard actually, and nobody could did it for 2 years or something until the Java Port appeared.