Screenshots / steps to fix Anonymous logon failure:

1. Open Central Administration site, navigate to Application Management->Manage Web Applications:

clip_image001

2. Select web application row and click on Authentication Providers ribbon button:

clip_image002

3. Cllick Default zone:

clip_image003

4. Ensure that Anonymous Access is turned OFF:

clip_image004

5. Click Save (even if no changes were made).

These steps should resolve the issue.