SQL Server Error 12450, Severity 17 typically occurs when an issue arises with an external data source connection (e.g., Polybase services attempting to connect, bulk insert operations, or linked server configurations). The error message associated with this code might vary depending on the scenario. However, Severity 17 indicates explicitly that the problem is resource-related or caused by environmental issues like memory constraints or connectivity problems between SQL Server and external components. This error would usually surface in scenarios where you're connecting to Hadoop clusters, Azure Data Lake Storage (ADLS), Oracle databases via linked servers, etc.

Common causes: 

• Polybase may fail to establish communication due to incorrect configuration settings for its head nodes and compute nodes. 
• External Connectivity Problems, Disconnected or misconfigured connections with external systems such as Big Data frameworks or cloud storage. 
• Environment Resource Constraints, Lack of sufficient system resources (CPU/RAM) while performing operations interacting with file systems/external data sources. 
• Network Configuration Issues, Blocked ports/firewalls affecting communications between subsystems.  

Retrieve and analyze all available information from logs (`ERRORLOG`) or client tools that describe what triggered error 12450. 

EXEC sp_readerrorlog;

Review patterns just before/after the occurrence of this specific error for any anomalies. Check System Resources Error severity 17 often points toward hardware/system resource exhaustion. Verify CPU usage and memory availability during peak processing times using:     

SELECT * FROM sys.dm_os_sys_info;