As much as I love crashplan it has been hanging with an error “Unable to connect to backup destination” lately. I poked around with google and it seemed to suggest an issue with Java not being able to access enough memory. Because I could not find the fix for a Mac I created a tech support ticket with Crashplan . They did get back to me and walked me though the following solution. Hopefully this can help others.
Launch a terminal window
Shutdown the crash plan daemon. You will be asked for your admin password. Go ahead and enter it here.
sudo launchctl unload /library/launchdaemons/com.crashplan.engine.plist
Now edit the plist file using the Unix Nano editor
sudo nano /library/launchdaemons/com.crashplan.engine.plist
Find Xmx512m and change it to Xmx1024m. This will allocate 1024mb of memory instead of the default 512mb
Save the file by Ctrl-O
Exit Nano by using Ctrl-X
Relaunch the Crashplan daemon (corrected Apr 19th 2012)
sudo launchctl load /library/launchdaemons/com.crashplan.engine.plist
This should fix the problem.