Fixits do not appear to work with this particular update failure. Please continue to use the manual instructions below.
And save the original keyboard layouts file with a different name. You can, for example, add a 1 to the registry file name so you have a backup. Now delete everything under the keyboard layouts key. Now save the edited regsitry file of Keyboard Layouts
(the original file name) into to the registry. You can click on the file and it will reimport it into the registry replacing the kbd files in the registry. (Please note that you may see this under Keyboard Layout (singular) - as well).
Now reboot your Windows XP.
Now attempt to install KB2686509 again either via manual download going to
http://www.microsoft.com/en-us/download/details.aspx?id=29804 and downloading from there or using Windows update again. It now should complete successfully.
If these instructions do not work for a Windows ME or Windows 98 upgraded to a Windows XP, please post back on
http://answers.microsoft.com/thread/0deeacb6-115c-419d-ac37-03ff8927b79c thread with your exact problem.