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