I ran into this same problem. It took over 8 hours to fully debug, and get my portals fixed.
First, check your DNN Users table for a Email column. Some how mine got deleted during the 3.0.13 upgrade.
Also check the stored procedures 'AddUser' and 'UpdateUser' for the email column.
Recompile the entire DNN3 application using nant or visual studio.net
This last step seemed to fix the issue, after I fixed the users tables the stored procedures, I was still getting the same error creating a new user, creating a portal or child portal.
Also, each time you tried to create a user/portal, the info was populated in the aspnet_ tables, if you tried to add a user, it will error out the DNN User Accounts module, because it saw a user in the membership users table, but can't find a match in the DNN users table.
I'm working on a SQL script that will automatically clean up the aspnet_* tables, fix the email column and stored procedures. However the rebuild of DNN I can't script. Check your dll's creation/modification date, all the DotNetNuke dll's should be very close to the same dates.