CrashPlan “Cannot connect to backup engine” errors on Mac OS X

I recently updated to Java 1.7 for work, and after doing so I noticed that CrashPlan was no longer performing backups. (I’m a bit ashamed to admit how long it took for me to notice though!) The company’s support forum suggests uninstalling and reinstalling the client, which didn’t fix the problem. A bit more searching identified the problem: CrashPlan expects Java 1.6, the official Apple version, and it gets unhappy if you replace that with 1.7. The instructions here outline a workaround: you have to stop the CrashPlan background service, modify its configuration file to point to the official-Apple version of Java, and then restart the service. Happy backups!