Duplicate errors but I don't have any duplicates. Will not import all users.

I have been trying to get this to work. I have about 40,000 users to import. I am able to see my file and match up the fields just fine and have set a special role for the incoming users. At first I tried to set the import to bring in all the users at once but I guess that was too much as nothing happened. So I went back to the default of 250 users per import. The first step went fine with all the users being imported. One odd thing is that the page I am taken to after import is 404 (admin/user/user_import/continue/2) but the users still get imported. I can see them when I go to the User Import page. The problems really start when I press Continue, this is where I start to get errors. At first there are just a few and I am still importing almost 250 users per press. But the errors start to build up. Now I am just over 19,000 users and clicking Continue no longer imports any new users. The weird thing is these errors are for duplicate emails but the CSV I am importing in does not have any duplicate emails. I have checked five different ones that User Import has given an error for and all are only in the CSV once. Another thing that is weird is the import page says it has only imported 9,000 users when it has done over 19,000. Also, the number of errors seems excessive. It says 13,149 processed, 9,000 imported and 389,663 errors all of which appear to be for duplicate emails which is crazy as there are only about 40,00 emails in total. It's almost like it is going through the same data over and over and seeing duplicates when really it is the same entry. I must be doing something wrong. Should I not hit the Continue Processing button? Do I wait for cron to pick it up? Is there a limit to how many I can import at once? I am not sending emails. I am 'activating' everyone on import and assigning a role. One final weird thing is that while most of the users that did get imported look perfect, the ones who only had an email address did not get assigned to the role. Only users who had at least one other field imported got assigned the role. This is the least of my worries, however, I would be happy to just have them all in there but I thought I would mention in case in helps figure this out.

I am sad, this is my second attempt where I spent a few hours hitting Continue Processing only to be left with an incomplete import which leaves me at square one. I did a little better this time - the first time I was only able to import about 13,000 names - still far short of all 40k.

I am using the latest version 6.x-2.3. I have read the instructions/documentation thoroughly, three times. I have looked through the issues and bugs and searched the forums but I haven't found anyone else with this particular problem.

This is not a live site. I do have a backup from immediately before the import that I can easily revert to. I just don't want to spend another late night getting nowhere so I'm hoping for some advice before my next attempt.

Thanks in advance for any help and for this module.

Jen