Error trying to install Unity Web Player in IE9

Anytime I try any of the Unity3D.com gallery demos in IE9 (WinVista), I am alerted that I need to setup before I can run.

So when trying to install the Unity Web Player, I receive this "Cannot Start Application" error dialog box: "Application cannot be started. Contact the application vendor."

Two buttons in the dialog box are "OK" and "Details ..."

If I press Details ... I get the following:

 PLATFORM VERSION INFO
     Windows             : 6.0.6002.131072 (Win32NT)
     Common Language Runtime     : 4.0.30319.296
     System.Deployment.dll         : 4.0.30319.1 (RTMRel.030319-0100)
     clr.dll             : 4.0.30319.296 (RTMGDR.030319-2900)
     dfdll.dll             : 4.0.30319.1 (RTMRel.030319-0100)
     dfshim.dll             : 4.0.31106.0 (Main.031106-0000)
 
 SOURCES
     Deployment url            : https://ssl-webplayer.unity3d.com/download_webplayer-3.x/3.0/co/UnityWebPlayer.application?installer=https%3A%2F%2Fssl-webplayer.unity3d.com%2Fdownload_webplayer-3.x%2FUnityWebPlayer.exe
                         Server        : Apache/2
     Application url            : https://ssl-webplayer.unity3d.com/download_webplayer-3.x/3.0/co/UnityWebPlayerBootstrap.exe.manifest
                         Server        : Apache/2
 
 IDENTITIES
     Deployment Identity        : Unity Web Player.app, Version=1.0.0.0, Culture=neutral, PublicKeyToken=3ba2843229693745, processorArchitecture=x86
     Application Identity        : Unity Web Player.exe, Version=1.0.0.0, Culture=neutral, PublicKeyToken=3ba2843229693745, processorArchitecture=x86, type=win32
 
 APPLICATION SUMMARY
     * Online only application.
     * Trust url parameter is set.
 ERROR SUMMARY
     Below is a summary of the errors, details of these errors are listed later in the log.
     * Activation of https://ssl-webplayer.unity3d.com/download_webplayer-3.x/3.0/co/UnityWebPlayer.application?installer=https%3A%2F%2Fssl-webplayer.unity3d.com%2Fdownload_webplayer-3.x%2FUnityWebPlayer.exe resulted in exception. Following failure messages were detected:
         + Unable to install this application because an application with the same identity is already installed. To install this application, either modify the manifest version for this application or uninstall the preexisting application.
 
 COMPONENT STORE TRANSACTION FAILURE SUMMARY
     No transaction error was detected.
 
 WARNINGS
     There were no warnings during this operation.
 
 OPERATION PROGRESS STATUS
     * [2/18/2013 9:01:04 PM] : Activation of https://ssl-webplayer.unity3d.com/download_webplayer-3.x/3.0/co/UnityWebPlayer.application?installer=https%3A%2F%2Fssl-webplayer.unity3d.com%2Fdownload_webplayer-3.x%2FUnityWebPlayer.exe has started.
     * [2/18/2013 9:01:04 PM] : Processing of deployment manifest has successfully completed.
     * [2/18/2013 9:01:04 PM] : Installation of the application has started.
     * [2/18/2013 9:01:05 PM] : Processing of application manifest has successfully completed.
     * [2/18/2013 9:01:05 PM] : Found compatible runtime version 4.0.30319.
     * [2/18/2013 9:01:05 PM] : Request of trust and detection of platform is complete.
     * [2/18/2013 9:01:06 PM] : Downloading of subscription dependencies is complete.
     * [2/18/2013 9:01:06 PM] : Commit of the downloaded application has started.
 
 ERROR DETAILS
     Following errors were detected during this operation.
     * [2/18/2013 9:01:06 PM] System.Deployment.Application.DeploymentException (Subscription)
         - Unable to install this application because an application with the same identity is already installed. To install this application, either modify the manifest version for this application or uninstall the preexisting application.
         - Source: System.Deployment
         - Stack trace:
             at System.Deployment.Application.SubscriptionStore.CheckApplicationPayload(CommitApplicationParams commitParams)
             at System.Deployment.Application.SubscriptionStore.CommitApplication(SubscriptionState& subState, CommitApplicationParams commitParams)
             at System.Deployment.Application.ApplicationActivator.InstallApplication(SubscriptionState& subState, ActivationDescription actDesc)
             at System.Deployment.Application.ApplicationActivator.PerformDeploymentActivation(Uri activationUri, Boolean isShortcut, String textualSubId, String deploymentProviderUrlFromExtension, BrowserSettings browserSettings, String& errorPageUrl)
             at System.Deployment.Application.ApplicationActivator.ActivateDeploymentWorker(Object state)
 
 COMPONENT STORE TRANSACTION DETAILS
     No transaction information is available.

(I have already uninstalled Unity and the Unity Web Player, but I continue to get this same error.)