Have you tried to transfer other scripts to the gateway? Assuming it is all scripts and not just this one that won't transfer, you'd need to check the access settings on the gateway itself, it might be restricted so that you can only see it/add it in OAMP but not allow file transfers like the script download.
If that's the case you'd either need to adjust permissions on the gateway or go to the gateway and pull the files over from a source, rather than use OAMP to do the transfer.
