"The application could not be installed because another application is already being installed" error

If you are running Windows, and get the error message "The application could not be installed because another application is already being installed. Complete the first installation before proceeding with this one." - you might have another application installer running.

Please see this the steps in this post to see if it resolves your problem.
http://social.answers.microsoft.com/Forums/en-US/vistainstall/threa...