Hi MattCan -
I have gleamed a little bit of information on what might be the problem with your Swarm Agent. To test this however, I want to make sure you have an absolutely clean no changes made to build of the engine. So, completely uninstall the engine (this should not remove your projects at all) and re-install from the Launcher Download.
Now, run Windows Update specifically looking for any Microsoft NET Framework updates and install them if any are found. Please make sure that the engine is installed before you run this update.
Test your Lighting Building Again on a new sample game type.
Thank you for your patience as we look into this issue and Let me know -
Eric Ketchum