Shaun, I had a similar injury from a similar piece of equipment. It can be a "repetitive stress injury." And it can be difficult to diagnose and treat. I ended up calling mine injury a "frozen shoulder." Best thing I can tell you is to not operate the screen machine anymore.
See if you can find out about PT and take that course of action to see if that will help you.
https://health.google.com/health/ref/Frozen+shoulder