From the Model Mayhem FAQ:

What can I do about these messages about non-secure sources? I can't edit my profile!
You may be seeing this when you go to edit your profile:

This error message is a result of using a non-secure image link (http://) in your profile's About Me, your Credit Note body, or your forum post. You will need to either update the image to a secure URL (https://) or remove the non-secure image link to successfully save the changes to your profile, credits, or to complete your post.

We discuss these changes to Model Mayhem in greater detail in our site-related thread.

If you continue to experience difficulty saving your changes, please let us know by clicking Help and contacting a moderator. Thanks!