Hello all, I am developing a C# application in VS 2010 that is to be deployed via ClickOnce. However when I try to deploy the application on a client machine I get the following error: Unable to install or run the application. The application requires the assembly Microsoft.VisualStudio.Shell.Interop.9.0 Version 9.0.0.0 to be installed in the Global Assembly Cache (GAC) first. I have tried to include the missing assembly into the application files under Project Properties-Publish tab, but the error remains the same. Next I tried to add Microsoft.VisualStudio.Shell.Interop.9.0 to the project's references, but I cannot find it in the reference list. Does anyone have any tips or solutions to this problem. Thanks in advance.