This could be something as simple as the PI Network Manager stopped running or could be a bit more involved. I would check to make sure PI Network Manager is running in services. You could also try to enable debugging as mentioned in the error message; this should provide some more information regarding why ProcessBook results in an error. Does this error occur upon opening the application or a certain display/displays in general? Additionally, what do you mean when you say "re-start" ProcessBook? Is this simply closing and re-opening, ending the process from task manager (or something similar), or reinstalling the program? If you would like to open a support call for this, just let me know.