How can I copy my existing forum and upgrade it to 4.0 Beta 3 to test?

What I did:

1) created new subdomain for new forum

2) imported DB from existing forum to new DB

3) copied /public & /uploads to new subdomain

4) uploaded IPB 4 Beta 3 to new subdomain

5) uploaded conf_global.php and updated data.

6) Started update, but gives me the following error:

An error occurred 
Location: Step 1. Application Core

 

 

This might help.

http://community.invisionpower.com/4bugtrack/beta-3-error-first-of-many-r403/