esmi on "Upload to Media Library"

Every time I attempt to upload a picture to the Media Library the screen displays 'HTTP error'. A friend, also with admin access, reports:-

"So if I try Media Tab on side menu, then Add New Item/Choose File/Upload after a while of waiting I get:
Sorry 84.92.55.109, your request cannot be proceeded. For security reason, it was blocked and logged.
If you think that was a mistake, please contact the webmaster and enclose the following incident ID:
[ #3287695 ]
Whereas if I use Library (i.e. Media Library) menu tab then I choose a file and it auto uploads but almost instantly it says:
IMG_0313.jpg
HTTP error.
IMG_01313.jpg being the file in the case but any file gives the error.
This also happens when creating a blog if I use the Insert Media option and then use the presented tab options: Upload Files"

I should add that the 'webmaster' must be a reference to myself.

Ahem: the site is http://www.greenfriends.org.uk

I originally thought the problem was to do with the memory quota for the site, but this has been investigated and is not the cause.

This is commonly caused by an over-aggressive configuration of your server's mod_security module. Try asking your hosts about it.

My ISP has whitelisted the IP's of my friend and myself, but it makes no difference.

Have spoken to your hosts about this issue and provided them with a copy of the error message?

I sent them the same material as quoted in my original message.

Thinks: there must be a log file which I can look at to explain the 'HTTP error.'

You could try checking your site's error logs but my guess would be that the only logs that might help you are server based and beyond your reach.