That typically means you're hitting POST input limits, broken HTML in one of the tabs, or a FORM element is embeded inside profile edit. How many fields do you have and are you using a lot of field group fields? If you're using Custom HTML fields be sure your HTML is valid and you don't have an unclosed tag somewhere. Be sure you're not trying to do something like render a tab inside profile edit that doesn't belong there (e.g. gallery tab or field, etc..). Does frontend profile edit save fine?