Mirror: gpg key issue

[H.S.Rai]

I tried to have a local mirror server using apt-mirror. One same same
machine, when tried to update system from this local mirror, I got
following error:

W: GPG error: http://192.168.7.9 feisty-updates Release: The following
signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive
Automatic Signing Key <ftpmaster at ubuntu.com>

I tried to use following solution, but fail to have success.

gpg --keyserver subkeys.pgp.net --recv KEY
gpg --export --armor KEY | apt-key add -

I don't know, if I need to replace subkeys.pgp.net with 192.168.7.9
i.e. IP of my mirror server. Should KEY in both above lines should be
same (which in my case should be 40976EAF437D05B5 )

May I know the way to remove this error.

Thanks in advance.

-- 
H.S.Rai
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