If you attempt to start the CrashPlan app and it gets stuck on the CrashPlan splash screen displaying the error, "Unable to connect to backup engine, retry?", this article can help troubleshoot the issue. Please note that this is usually because the CrashPlan service is not running; it is not a network error.
The CrashPlan app consists of two parts: the graphical user interface that the user interacts with and the CrashPlan service that runs in the background. These two pieces communicate over a local network connection that is built into every computer. When the CrashPlan app starts, the CrashPlan service attempts to connect back to itself. If it can't connect, the backup engine won't start.
The more data included in the backup file selection, the more memory CrashPlan requires. File selections that contain a large amount of data (>1 TB) and/or a large number of files (1 million+ files) may require more memory than CrashPlan's default memory allocation (512 MB). When CrashPlan runs into this memory limit, the background service crashes, resulting in the "Unable to connect to backup engine" message. If you have a large file selection backing up, refer to our troubleshooting article on this topic to address the issue.
The CrashPlan.app file must reside in the Applications folder and must be named CrashPlan.app. If you've moved or renamed CrashPlan.app, you may see the “CrashPlan unable to connect to the local backup engine” error upon starting the CrashPlan app. To resolve this, uninstall and reinstall CrashPlan.
The CrashPlan app version 3.4.1 and earlier is not compatible with Java 1.7. On October 16, 2012, Apple released an update to Java 1.6 that could cause your computer to use Java 1.7 by default. This WikiHow article can help you determine which version(s) of Java are installed on your computer.
Is the CrashPlan service enabled? You can verify this from the Microsoft Services menu. To open the Microsoft Services menu:
If the "Unable to connect to backup engine" error returns after each reboot, this is usually caused by another Windows service conflicting with the CrashPlan service at boot. To resolve this, you can delay CrashPlan's startup. To do this:
Finally, if you're still having troubles, you can test to make sure that nothing else on the computer is already using ports 4242 and 4243, which CrashPlan needs to run. CrashPlan may not need to use these ports all the time, but it still needs to prepare them for use (open the socket).