Why does Windows report that files stored on my NAS might be harmful when I try to copy them?

Question

Scenario

My NAS drive (a Synology DS214+) not working on a domain, with multiple clients connected on the domain.

Network drive mounted and can be accessed, however copying files gives the following error:

This error was not present when the NAS drive was part of the domain, however this is no longer possible.

Question

1: Am I right in assuming that this error is because the NAS drive is not part of the domain, and the domain client is trying to access files?

2: Is there any other option to fix this other than rejoining the domain?

Update

• Mapping via the IP address or hostname makes no difference

Answer 1

To answer your questions...

1. Am I right in assuming that this error is because the NAS drive is not part of the domain, and the domain client is trying to access files?
   
   This error is probably caused by Windows thinking you're copying stuff from the Internet and not the intranet and depending on the security settings for the zone (probably the Launching applications and unsafe files setting?) it is prompting you to confirm the transfer.
   
   

2. Is there any other option to fix this other than rejoining the domain?
   
   Yes. Add the IP address of the NAS drive to the Local Intranet zone. Bring up Internet Options by pressing Win+R → control /name Microsoft.InternetOptions → Enter
   
   Then follow Jeff Atwood's instructions:

   • Click Security tab.
   • Click Local Intranet
   • Click Sites button.
   • Click Advanced button.
   • Enter the IP Address of the other machine or server (wildcards are allowed) and click Add
   • Click Close, then OK, then OK again.