Archived ⇒ Some users cannot login after an upgrade.

The easiest fix I found for the illegal mix of collations:
1] export your database using phpMyAdmin
2] open the file in a text editor and change any latin1_swedish_ci to utf8_general_ci
3] create a new database (make sure default collation is utf8_general_ci)
4] import the edited backup
5] point your df install to the new database

This will take care of any tables that have mixed fields and all the tables...