I received an odd error message while attempting to add an item template contained within a project to my VSIX file through the manifest editor.

Here are the steps to get to this error. Open the vsixmanifest file. Add content. Select Item Template, choose a project, then press ok.

This error is one of incorrect parameters. The correct solution is to use the file option, which allows you to select an ItemTemplate zip file. This places the zip file in the ItemTemplates folder of the project. Unfortunately, this means you will need to set up an process to copy the zip file into the ItemTemplates folder, as it will not be update when changes are made to the files that make up the item template.