I had a similar problem with a Wireshark startup script.
Try running the following:
sudo xattr -r -d com.apple.quarantine /Library/StartupItems/ShhMBP
This will remove the com.apple.quarantine attribute that the OS is setting on files which have been downloaded from the Internet.
If you want to confirm that this is the problem before running the above command, the run "ls -l -@ /Library/StartupItems" and look for the com.apple.quarantine attribute on your folder.
Hope this helps!