🎮 Common Scenario: Are you experiencing Error 1748 while launching or installing AutoCAD? The solutions below directly address the system interactions specific to this application.
Restart RPC Services: Press Win+R, type services.msc, press Enter
👇 See all 2 solutions belowThe Ultimate Auto-Fix Script
Download our advanced, custom-built Smart Diagnostic Script (.bat). It safely creates a System Restore Point, applies targeted fixes based on advanced diagnostics for Error 1748, and generates a detailed HTML repair report.
What is Error 1748?
Windows System Error Code 1748, known as RPC_S_UNKNOWN_AUTHN_LEVEL, is a RPC & Network error that occurs during Remote Procedure Call (RPC) and network communication. The error indicates that: The authentication level is unknown. When this error is encountered, the Windows operating system was unable to complete the requested operation within the network services subsystem. The error code 1748 is returned by the GetLastError() function and provides developers with a specific identifier to diagnose the root cause of the failure. The symbolic name RPC_S_UNKNOWN_AUTHN_LEVEL maps directly to this numeric code and is commonly referenced in Microsoft documentation, developer forums, and system logs. Understanding this error and its context within Remote Procedure Call (RPC) and network communication is essential for effective troubleshooting.
Common Causes
- RPC service or its dependencies (DCOM, Endpoint Mapper) are stopped
- Firewall is blocking RPC ports (135 and dynamic range 49152-65535)
- Network connectivity issues between client and server
- Active Directory or DNS issues preventing server discovery
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Read the full guide →Step-by-Step Solutions
- Press Win+R, type services.msc, press Enter
- Find 'Remote Procedure Call (RPC)' — ensure it's Running and set to Automatic
- Also check 'RPC Endpoint Mapper' and 'DCOM Server Process Launcher'
- If stopped, right-click each → Start
- If they won't start, run: sc config RpcSs start=auto from Admin CMD
Video Tutorials
Diagnostic Command
Run this PowerShell command to find related events in your system log:
Get-EventLog -LogName System -Newest 20 | Where-Object {$_.Message -like "*1748*" -or $_.Message -like "*RPC_S_UNKNOWN_AUTHN_LEVEL*"} | Format-List💡 Open PowerShell as Administrator, paste the command above, and press Enter.
Prevention Tips
- Never disable the RPC service — many Windows features depend on it
- Monitor service health using: sc query RpcSs periodically
- Ensure DNS is properly configured for domain-joined computers