Check your link for responseRedirect, and be sure it is typed correctly:
if an Admin Link:
return $this->responseRedirect(
XenForo_ControllerResponse_Redirect::SUCCESS,
XenForo_Link::buildAdminLink('where-i-should-redirect-to')
or Public Link:
return $this->responseRedirect(
XenForo_ControllerResponse_Redirect::SUCCESS,
XenForo_Link::buildPublicLink('where-users-should-redirect-to')
);