Well after wrestling with this for over two hours I think I have found my issue, I had previously changed my password. Apparently Impulse/Stardock stores your un/pw in two different locations. You need to change it in the Community area AND in the Impulse app.

I completely uninstalled Impulse. Re-downloaded the app, installed it and then was greeted with an "Invalid username/password" message as well as a dock icon for Impulse. My un/pw worked fine in the Community area but for whatever reason it didn't work with updates.

I left-clicked on the dock icon and was able to select "Check for updates" then, once in Impulse you can click on the lightning bolt in the upper-left corner and select Log-in. This will allow you to put in the correct credentials.

Clear as mud?

Did they have trained monkeys designing this UI?