I'm in EU, been attempting to patch tonight and getting this everytime; never experienced it before.
The patch "enGB\DBFilesClient\Item.dbc" could not be applied. (Invalid source file size: expected 1475061, actual 2162741.) If this problem persists, you may be able to solve it by uninstalling and then reinstalling the game. If you are unable to correct this problem, please contact Blizzard Technical Support. (BNUpdate::PTCApply)
To check this installation for problems, click the "Repair" button. The Repair tool can automatically fix many update errors.
I had previously been changing my game files to log onto US servers, but would run a WoW Repair to revert back to EU, I don't know if that would have had some kind of affect on my files, I have ran a WoW Repair since I last did that though and haven't changed anything major since my last WoW Repair (No new add-ons/patchs/installs or anything)