When I authorize a new registered user or add a security role the site no longer generates an e-mail that is sent to the user telling them they now have access. This used to work and it just stopped, anyone have any ideas what could be the problem?

Did you do any upgrades?

If you have host access, check the smtp settings. Try sending a test email.

If the test email arrives, it may be that whomever controls the smtp server has changed something. Check to see that the messages from DotNetNuke are getting to the SMTP server (the administrator of that system can check logs).