changing email of user via admin interface throws exception

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This is what I see as error

IntegrityError at /admin/auth/user/2/ update or delete on table "auth_user_groups" violates foreign key constraint "authusergroups_ptr_id_refs_id_e728db87" on table "askbot_groupmembership" DETAIL: Key (id)=(5) is still referenced from table "askbot_groupmembership".

Is it not possible to change the email address of user via admin?