Help - can't install "Specified cast is not valid"

Hi,

I've tried installing the demo version of Organiser, but after the Outlook Add-in installer opens, I get the error "Specified cast is not valid", followed by the following error. Any ideas? I'm running Outlook 2007 on Windows 7.

Thanks,

Oliver.

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************** Exception Text **************

System.InvalidCastException: Specified cast is not valid.

   at Microsoft.VisualStudio.Tools.Applications.Deployment.ClickOnceAddInDeploymentManager.GetManifests(TimeSpan timeout)

   at Microsoft.VisualStudio.Tools.Applications.Deployment.ClickOnceAddInDeploymentManager.InstallAddIn()