When using Joined Date & Last Login Date custom fields in a profiletype, it is impossible to create a new user from the backend of easysocial (easysocial-->users-->new)
They are not filled in when creating a new user and cannot be filled in by the admin. Therefor on save of the user, You will get the error: "There was some error in your form. Please correct the respective fields. "
Probably those custom fields are set to required. Because they are emtpy when creating new user from the backend it is impossible to create a new user with those custom fields in the profiletype.
small note: not a big problem, cause new user registration via frontend goes fine with those custom fields enabled in the profiletype.