I gave a presentation on ClickOnce and XBAPs at the VBUG Conference recently and I had a "Its never done that before" moment as ClickOnce failed to deploy. I was floored. It was my first demo in a presentation all about ClickOnce so it was difficult to ignore it and keep going. In the end I switched to a virtual machine and continued the presentation from there. However, that just avoided the problem instead of fixing it. The symptom, for the curious, is that after publishing the ClickOnce application and clicking on the Install button in publish.htm ClickOnce insists that the .NET Framework 2.0 is not installed (despite the deployment being performed on the same machine that Visual Studio 2005 published the app from and therefore had to have the .NET Framework 2.0 installed). publish.htm then offers to install the framework with "Would you like to download and install the Microsoft .NET Framework ?".

The answer comes courtesy of John Sinclair via Julie Lerman via Brian Noyes (the author of the excellent Smart Client Deployment Using ClickOnce) in Julie’s blog post ClickOnce on Vista installation problem SOLVED!. In essense the .application file association was pointing to the wrong application. Thanks, Brian, Julie and John.

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