Hi Aderson,
it seems that enabling 'allow email address with password reminder' upsets things.
http://www.dnnsoftware.com/community/learn/video-library/view-video/video/97/view/details/enable-forgot-password-using-your-email-address-in-dotnetnuke
I switch back requiresUniqueEmail="false" in web.config then it works again.
I thought it would be useful for our users - but not essential so switched back to user name only - maybe try again in a later DNN release.
Thanks for your advice as allways.
Richard