Filesync Error: "Macintosh HD is full or read-only."

I am using FileSync to sync between an SMB file share on my linux desktop and a folder on my MacBook's HD. I click the sync button, and sometimes a few seconds in it will stop and give the following error message: "Macintosh HD is full or read-only." My HD is no where near full, and isn't read only either. Plus, it has usually already synced one or two files. Sometimes, though, it goes through with no error. What could be the problem?