deny updating a hidden ref

gitlab使用镜像方式同步另外一个gitlab仓库步骤如下:
1.git clone --mirror
2.sed -i -r ‘s/(url =).//url = git@*****//’ config
3.git push --mirror(报错步骤)
异常信息如下,这是什么原因呢:
! [remote rejected] refs/merge-requests/1/head → refs/merge-requests/1/head (deny updating a hidden ref)
! [remote rejected] refs/merge-requests/2/head → refs/merge-requests/2/head (deny updating a hidden ref)
! [remote rejected] refs/merge-requests/3/head → refs/merge-requests/3/head (deny updating a hidden ref)
! [remote rejected] refs/merge-requests/4/head → refs/merge-requests/4/head (deny updating a hidden ref)
! [remote rejected] refs/merge-requests/5/head → refs/merge-requests/5/head (deny updating a hidden ref)
! [remote rejected] refs/merge-requests/6/head → refs/merge-requests/6/head (deny updating a hidden ref)
! [remote rejected] refs/merge-requests/7/head → refs/merge-requests/7/head (deny updating a hidden ref)
! [remote rejected] refs/merge-requests/8/head → refs/merge-requests/8/head (deny updating a hidden ref)
error: failed to push some refs to '
******’

第一步将git clone --mirror 改成git clone --bare试一下。