To obtain the connection string, wasp has to be able to contact the data_engine on the Primary hub, and afterwards, it also needs to contact the DB server machine directly.
Make sure the wasp robot can resolve and reach both machines, using ping, tracert, nslookup etc.
Test direct access to the DB server via telnet <DB_SERVER> <port>
e.g., telnet <db_server_host> 1433
The data_engine provides a connection string for other probes so they can connect to the data_engine, e.g., wasp, nas, etc.
These probes persist their own data in the database and they use their connection strings to do so. The string is the same across these probes. These probes only need to obtain the data_engine connection string once when they startup. If the connection string changes, e.g., due to the database password being changed and the data_engine is restarted, then the wasp probe will not be able to connect to the database.
To remedy this you can delete the connection string via wasp via Raw Configure, and then restart it and it will reset its connection string.
If the string changes, you have to restart the probes that rely upon their particular connection strings so they can connect to the data_engine.
In the case of wasp and nas, if the connection string changes for any reason, you must delete the connection string using Raw Configure and cold start (Deactivate-Activate), the wasp/nas probe so it picks up the new connection string and stores it.