Share your experience!
Hi.. i just get this new handphone (Xperia Z) this few day.. my Problem is:
**when i what to active my "WhatsApp" the message like said my version is to old and need upgrade, so i try to download this new application from "Play store" but error ("WhatsApp Messenger" could not be downloaded due to an error (923)) , can u help me to settle this problem?
completely remove/unuistall the whatsapp you have installed
remaove any task killers memory managers antivirus firewalls etc etc and do not install this type of software again they create issues and solve none - if you don't have any great
Remove SD card if you have one
try again to download and install WA - if it still fails try downloading another app
then report back 
Also send this error report to whatsapp support they will surely help you
Send them a mail on [email protected]
if it still remains then do a repair with sony update service.
http://www.sonymobile.com/gb/tools/update-service/
Remember to do a back up of your files first then do a repair.