Outlook web-addin open external application with registered scheme

I'm developing an outlook add-in that's based on an existing web page I already have working (so mostly changing UI to fit the look and feel I want). In the task-pane I open I have a "launch" button that I use to launch an external application. The application already has a specific scheme registered and I can launch it when I get to the web page via the browser, but when I click through the task-pane nothing seems to happen.