To solve any error first you need to find out the error details. See Basic Troubleshooting.
Things like userid and security question and answer are not custom profile properties they are part of the security and account system. You can opt to not show the security question and answer from Site Settings > Security it will just be populated with default question and answers if you do that so that it is not empty if you ever turn it back on.
All accounts must have both a unique login name and email address. If you are using email for login you can hide the login name (user id) on the registration page and populate it automatically but it will still be visible on the user account profile.
Put this in user.config if you want to not autogenrate the user login name and not show it during the registration:
<add key="AutoGenerateAndHideUserNamesWhenUsingEmailForLogin" value="true" />
You should not modify mojoPortal code, you should not try to change urls or file names for .aspx files that are part of mojoPortal that is equivalent to forking the code and we cannot provide support for forked versions of the code.