The message “Unable to connnect to the local backup engine” means that the PRO Client Desktop is unable to communicate with the PRO Client service on localhost:4243. This error refers to internal communication within the client computer and not external communication between PRO Client and PRO Server.
The first thing is to try restarting the backup engine.
If there are any software firewalls or other security software installed on the client computer, make sure an exception has been created for the PRO Client.
The full path to the CrashPlan.app file must be /Applications/CrashPlan.app. If you've moved or renamed CrashPlan.app, you may see the “Unable to connect to the local backup engine” error upon starting the CrashPlan desktop. To resolve this, uninstall and reinstall CrashPlan.
If you are still having trouble, please send support your log files and include a description of the problem in your message.