I’m not sure what you mean by boxes, but the Worker beacon permission does not allow players to add or remove blocks with a beaconed area, but will allow them to interact with beacon controls, machines, storage blocks, beacon controls and anything else that displays a GUI menu upon interaction. Items can be added to or removed from the GUI menus.
It could be possible that sloped blocks might have caused the issue. We have fixed some bugs where making contact with such blocks may cause characters to appear somewhere else all of a sudden, so this should be in the next update.
The log seems to suggest that a graphics driver is crashing. The screenshot of Fatal Error 29 is different as it suggests that Steam may not be running correctly. Try restarting or updating Steam.