Yes, that helps. From the log you posted above, it appeared that (for whatever reason) your database's "Create Account Default Country" was an empty string instead of a numeric value and I reproduced the error you posted by changing my test site's value to an empty string!
You can correct your issue by going to the admin's Tools :: Install SQL Patches and entering the following to set that country default to Australia:
Code:
UPDATE configuration SET configuration_value = '13' WHERE configuration_key = 'SHOW_CREATE_ACCOUNT_DEFAULT_COUNTRY' LIMIT 1;
P.S. I have no idea how that empty value has worked for so long!