You don't really need to investigate the code though, if you just want to understand errors.
In this case, if you take a look at the error message, it says "Failed to connect to worker process" -- calibre uses worker subprocesses to do various tasks, and this is a well-known sign by now that some antivirus is blocking calibre.
Of course, to know that you'd have to hang out here a lot and see many people have that problem.
