rob.parkin390637 and biz295654, most likely the Email Password server behavior is set to use the wrong database column as the Look up column on the database tab.
go to the server behaviors panel, double click the Email Password server behavior, then go to the database tab and make sure the Lookup column is set to use the Email address column.
if you continue to have problems, send a copy of the forgot password page so I can look at the code.