App store sign in dialogue not responding

Question

Since upgrading my iMac to Mavericks I have received various upgrade notifications and successfully upgraded several apps.
However my Pages app is under a different apple id and is listed as having an upgrade ready, but when I try to sign into the App store with that id the sign in dialogue box just sits there with the activity icon circling and nothing happens.
I can sign in with that id to iTunes and store.apple.com/au etc, and have changed my password and contact email successfully, but I can't use the id to sign in to the App store, the dialogue box just sits there doing nothing.
I've tried shutting down, logging off, closing iTunes and App store, etc. This has been going on for over a week.
Could someone suggest a solution to this problem?

Answer 1

Back up all data.
Triple-click anywhere in the line below on this page to select it:
~/Library/Cookies/com.apple.appstore.plist
Right-click or control-click the line and select
Services ▹ Reveal
from the contextual menu.* A folder should open with an item selected. Quit the application if it's running. Move the selected item to the Desktop, leaving the window open. Relaunch the application and test. If there's no change, quit again and put the item you moved back where it was, overwriting the one that may have been created in its place. Otherwise, delete the item you moved. If possible, restore it from a backup that predates the problem.
*If you don't see the contextual menu item, copy the selected text to the Clipboard by pressing the key combination  command-C. In the Finder, select
Go ▹ Go to Folder...
from the menu bar, paste into the box that opens (command-V). You won't see what you pasted because a line break is included. Press return.