CrashPlan.app somehow make its app folder not immutable, so that sometimes it causes problem when deleting it from Time Machine backups.
I am somehow having problem on El Capitan 10.11 beta that local Time Machine backups are taking all my spaces. So I disabled it but have problem emptying the trash. And it is CrashPlan.app.
This is the command to use:
> chflags noschg CrashPlan.app # this removes system immutable flag
> chflags nouchg CrashPlan.app # this removes the user immutable flag
In my case I used chflags -R noschg/nouchg .Mobilebackup.trash
Finally got my SSD space back.