NTFS folder permissions are not set correctly.
The Command folder requires that "Everyone" in the network have "Full Access" to work correctly.
Navigate to the Install Directory, then Symantec Endpoint Protection Manager\data\outbox\agent\
Right click on the "command" folder and confirm that "everyone" has "full control" access to this folder.
Make sure that the sub-folders inherit permissions, and "Read only" is not checked.