I am also working on the course. I had a similar error at the same step as yours so I want to share to see if it can help you.
In the step modifying the Interaction-Call.xml, I copied directly from Pega training website. So instead of double quotes ", it has “”. That is why I got the error " Error loading 'Main-UI_Debug.OpenSpan' '“' is an unexpected token... ". Then those errors you mentioned come up.
To fix it, as Sasnt mentions, end all "Pega.Runtime" process, correct the double quotes, clean the solution, then build the solution. The problem is solved.