This issue is caused by the system trying to register and update the Accepts Email field (bug 69587).

The constituent's record is currently listed as blank, rather than the expected Yes or No.  A selection needs to be made to correct this error.

You can build a query to display the constituents who have null emails.
  1. Data Management, Query
  2. Create New Query
  3. Enter Name and Description
  4. Field Type: select Email
  5. Field: select Accept Email
  6. Click Add Field Clause
  7. Set "Accepts Email" to equal "blank"
  8. Field Type: select Email
  9. Field: select Email
  10. Set "Email" to equal "is not blank"
Save and run this query, and then you will have a working list of users who may be affected.