Problems with manual update

I have been getting an error message when I try and do a manual update check.
I have applied all the advice given by the update site to no avail. On
checking my Security Centre, I now have an error message saying that the
Centre is not switched on or has stopped. Mean while the auto update system
is working quite well with updates downloading as I type! While I am in no
danger of not getting the updates, I am concerned that something, somewhere
is wrong!
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David Harding