OK, this is no longer a coincidence: All CrashPlan users should please check the free space on your Macs’ hard drives.
On your desktop, click on “Macintosh HD,” then go to the File menu > Get Info…
If the Space Available looks low, say less than 10 GB, it might be that (pardon the expression) a CrashPlan log has grown unusually large. Open up Macintosh HD > Library > Logs > CrashPlan, and look for engine_output.log. See how big it is. I’ve now seen 30 GB, 80 GB, even 600 GB.
Throw engine_output.log in the trash, and empty your trash (right click on the trash can or Finder menu > Empty Trash…).
If the trash won’t empty, restart your Mac and try again.
Perhaps your hard drive is full for other reasons, in which case the excellent freeware Disk Inventory X can help: http://www.derlien.com/downloads/index.html
jjmarcus tech solutions 
Most CrashPlan log files are capped, so seeing a log of this size is weird. It may actually indicate another issue with the CrashPlan application. Our Customer Champion team can check for you. You can chat/email/call – instructions at support.crashplan.com/#get_help
We’ve most frequently seen this when the CrashPlan application is running out of memory, causing Java errors. The way to check/fix this is described in this article:
https://helpdesk.crashplan.com/entries/22855142-CrashPlan-continuously-crashes
We’d love to help, so let us know if you have any questions, let us know.
Ryan at Code 42, makers of CrashPlan
Thanks for that, Ryan! I do make that maximum-memory adjustment as a matter of course, as well as the 32-bit Java restriction, outlined in this oft-referenced post, for all of my CrashPlan users. I am pretty sure that the people who called me, prompting my post, had those adjustments to the plist in place. But I will double-check that, and will contact your team if the problem recurs.