I thought I was loosing my mind when I could not get the one page checkout to work on my site when upgrading to 5.5.0.0 from 4.0.0.0. So I went back and performed a new installation on a Windows 7 (x64) machine using KonaKart-5.5.0.0-Windows-Setup.exe. I created a fresh/empty database and let Konakart populate the database with the demo data.
Launching the demo site and checking out (all using localhost:8780 demo site created by KonaKart with no changes made in KonaKartAdmin) I attempt to checkout using a new email address. I am then prompted for checkout information (name, address, country, etc). After entering a password and clicking 'continue', nothing happens. Click 'continue' again and the error pops up that says this email address already exists. It is impossible to move past this screen.
My environment:
Windows 7 (x64) sp1
Mysql 5.5.15 (x64)
JDK 1.6.0_23 (x64)
No changes or extra libs added. Just run right after install with the default store.
You can see the same problem trying to checkout of the konakart demo site. Just make sure you try to checkout as a 'new' customer (using an email that is not already in the system).
Yes, we have been able to reproduce. Thanks for reporting this problem.
See a code fix in this thread:
http://www.konakart.com/forum/index.php/topic,1545.msg6125.html#msg6125
This will be fixed in 5.5.0.1 which should be available within the next few days.