Issues with upgrading
If you followed all the steps, I assume you have (or can get) a working copy of original 6.x page.

The question is - are your nodes OK?


If they work properly, it means you have data in good enough state. Delete views that include problematic fields and recreate them from the ground. Optionally export them, remove fields that cause problems from exported file, delete from server, import and add fields. That's the easy case
Sadly, if there was changes in the fields you were using in the very nodes, that renders nodes unusable, it will be worse. You will need to export data from 6.x site to some more or less universal format, like csv or xml, and import it anew to 7.x 


Delete migrated data and it's content type
Create new content type with new-style fields, that maps 1:1 to old node structure. If possible, keep names
Export node data, using Node Export, Views data export or similar tool
Secure all the files referenced by nodes
If needed, manually upload secured files to new version; see next step
Import nodes using tool like Node Export or Feeds - it may be required for files to be already uploaded, read the manual of your importing tool