If RDB is installed locally and the SQL server support managed by a third party, we would advise you raise this issue with your local IT Support to investigate.
The cause of this issue is that the local computer cannot create a connection to the SQL server. This error could be due to one or a combination of the following;
the server is offline.
changes have been made to the internal network.
network connectivity issues on the local device.
If a user is working remotely and is getting this error then your IT will need to setup a VPN (virtual private network). A VPN allows you to create a secure connection to your office network over the internet.