Update manager reports updates of packages 404 on the mirror

Update manager popped up proclaiming there were 13 updates. However, after being told to go ahead it said misleadingly "check your internet connection" because the packages were missing on the server. This isn't the first time this happens. It's kinda annoying when you know the problem is too slow mirroring (and the update notifier not checking first) but for some newbie this could be fairly off-putting.

The details button reveals the actual cause:

Failed to fetch http://ftp.rediris.es/mirror/Trisquel/packages/pool/main/l/linux/linux-image-3.0.0-22-generic_3.0.0-22.36+5.5trisquel1_amd64.deb 404 Not Found Failed to fetch http://ftp.rediris.es/mirror/Trisquel/packages/pool/main/a/accountsservice/accountsservice_0.6.14-1git1ubuntu1.2_amd64.deb 404 Not Found Failed to fetch http://ftp.rediris.es/mirror/Trisquel/packages/pool/main/a/accountsservice/libaccountsservice0_0.6.14-1git1ubuntu1.2_amd64.deb 404 Not Found Failed to fetch http://ftp.rediris.es/mirror/Trisquel/packages/pool/main/n/network-manager/libnm-util2_0.9.1.90-0ubuntu5.2_amd64.deb 404 Not Found Failed to fetch http://ftp.rediris.es/mirror/Trisquel/packages/pool/main/n/network-manager/libnm-glib-vpn1_0.9.1.90-0ubuntu5.2_amd64.deb 404 Not Found Failed to fetch http://ftp.rediris.es/mirror/Trisquel/packages/pool/main/n/network-manager/libnm-glib4_0.9.1.90-0ubuntu5.2_amd64.deb 404 Not Found Failed to fetch http://ftp.rediris.es/mirror/Trisquel/packages/pool/main/n/network-manager-applet/libnm-gtk-common_0.9.1.90-0ubuntu6.1_all.deb 404 Not Found Failed to fetch http://ftp.rediris.es/mirror/Trisquel/packages/pool/main/n/network-manager-applet/libnm-gtk0_0.9.1.90-0ubuntu6.1_amd64.deb 404 Not Found Failed to fetch http://ftp.rediris.es/mirror/Trisquel/packages/pool/main/l/linux-meta/linux-image-generic_3.0.0.22.26+5.5trisquel1_amd64.deb 404 Not Found Failed to fetch http://ftp.rediris.es/mirror/Trisquel/packages/pool/main/l/linux/linux-libc-dev_3.0.0-22.36+5.5trisquel1_amd64.deb 404 Not Found Failed to fetch http://ftp.rediris.es/mirror/Trisquel/packages/pool/main/n/network-manager/network-manager_0.9.1.90-0ubuntu5.2_amd64.deb 404 Not Found Failed to fetch http://ftp.rediris.es/mirror/Trisquel/packages/pool/main/n/network-manager-applet/network-manager-gnome_0.9.1.90-0ubuntu6.1_amd64.deb 404 Not Found Failed to fetch http://ftp.rediris.es/mirror/Trisquel/packages/pool/main/p/python-crypto/python-crypto_2.3-2ubuntu0.1_amd64.deb 404 Not Found