Within Tools > Operation > Downloads you see that "Specific Distribution Server" is grayed out under Definition download source, and you do have distribution sever(s) configured in this Protect console already.
1) You do not have a Distribution Server configured, or;
2) Your Distribution Servers are set up with at least one scheduled automatic synchronization tasks.
(Distribution Servers set up with automatic synchronization cannot be used a definition download source.)
1) Ensure that you have at least one Distribution Server configured within Tools > Operations > Distribution Servers.
2) Ensure that the Distribution Server you intend to use as a definition download source is not configured for any Scheduled automatic synchronization under Tools > Operations > Distribution Servers.
Be aware that if you are intending to use a Distribution Server (share) as a definition download source - this share must be getting new data copied into it from a separate console that has an internet connection.
Refer to the following documentation for more information:
Shavlik Protect 9.x