What does Windows error code 746 (ERROR_PRIMARY_TRANSPORT_CONNECT_FAILED) mean?

ERROR_PRIMARY_TRANSPORT_CONNECT_FAILED

Connection on the preferred transport failed and Windows may try another

ERROR_PRIMARY_TRANSPORT_CONNECT_FAILED corresponds to Win32 error value documented as: {Connect Failure on Primary Transport} An attempt was made to connect to the remote server %hs on the primary transport, but the connection failed. The computer WAS able to connect on a secondary transport. The primary network transport could not establish the requested server connection. Some legacy networking paths can fall back to a secondary transport, so the final outcome depends on later attempts.

Where the result appears in real systems

• Multi-transport redirector logic.
• Legacy SMB or RPC networking.
• Environments with disabled protocols or mismatched bindings.

What to collect before making changes

Preserve server name, primary transport, endpoint, address family, and subsequent fallback result; collect DNS output, routes, firewall logs, and a packet trace; verify whether policy intentionally disables the preferred transport.

Handling and recovery

Use a supported transport and correct its reachability or binding. Do not declare the server unavailable until the API contract confirms that all permitted fallback attempts have failed.

What not to infer from this code

This code isolates failure of the primary transport, whereas a generic network-unreachable result says nothing about an available secondary path.

References

• Microsoft: System error codes 500–999