The Symantec Management Agent requires enough disk space available to download policies and save credentials.
Under investigation. Unfortunately there seems no easy fix because even if the disk is full there is no way a storage can be modified without "dirty mark" file modification which requires a few bytes. Seems that more general solution with some disk reservation for emergency cases is needed.
ITMS 8.1 RU6 and later
Current workaround is to switch to using a local ACC account and free disk space.
Also, please refer to INFO5222 "How the 'Re-enable the created local account if it has been locked out' setting works"