Cannot install ClickOnce - Certificate Not Trusted

Question

I am trying to publish a small Microsoft Office customization using Visual Studio 2013. I purchased a code-signing certificate from GoDaddy (issued by Starfield Technologies) and used it to sign the program. However, when a user tries to install the ClickOnce Manifest, they get the following error:

Customized functionality in this application will not work because the certificate used to sign the deployment manifest for RiskMP or its location is not trusted. Contact your administrator for further assistance.

The program is being downloaded from the same server from which the private key was generated and the same URL that was specified in the publish.

The only solution I have found so far is to add the URL to the list of trusted sites in IE internet options, but this isn't a very good solution as it requires a lot of steps on the part of the user. I'd like to simplify this installation as much as possible. Any help is greatly appreciated.