Why am I getting an error when trying to install a ClickOnce application behind a firewall?

You may experience the following message when you are behind a firewall and using ClickOnce:

The remote server returned an error: (407) Proxy Authentication Required.

ClickOnce currently has a bug which doesn't allow users behind a firewall to download and install the application.

The root cause is that .Net deployment API did not use the default proxy and credentials to access the remote clickonce files. To workaround this issue, we can set useDefaultCredentials to true in machine.config, like this:

<defaultProxy enabled="true" useDefaultCredentials="true">

But we don't want this for our whole site, so if you are behind a firewall, you can download the hotfix which requires the .Net Framework 2.0. Note: You may need a restart of your PC after installation of this hotfix.
You can also read the microsoft support page for this particular issue.
Microsoft recommends that you wait for the next .NET Framework 2.0 service pack that contains this hotfix.

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Keywords: SSW Diagnostics  Hot Tip - VB.NET (Winforms)    

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