This may be due to the configuration of the Standard Page Center. To verify this:
  1. Go to Setup Standard Page Center.
  2. Click Customize next to Constituent Profile (Admin-Side User Registration).
  3. Go through the on screen prompts to verify the configuration.
  4. Once completed, click Customize next to Constituent Profile (Admin-Side User Update).
  5. Go through the on screen prompts to verify the configuration.

If that does not resolve the problem, contact support.