2dust/v2rayN · error · ApplicationException

Set Internet Proxy failed with error code: {Marshal.GetLastW

Error message

Set Internet Proxy failed with error code: {Marshal.GetLastWin32Error()}

What it means

Thrown after the WinInet InternetSetOption/InternetSetPerConnOptions call sequence returns a non-zero (failure) result. The message appends Marshal.GetLastWin32Error() so the Win32 error code is visible. It signals Windows declined to apply the system proxy configuration.

Source

Thrown at v2rayN/ServiceLib/Handler/SysProxy/ProxySettingWindows.cs:194

        // FREE the data ASAP
        if (list.szConnection != nint.Zero)
        {
            Marshal.FreeHGlobal(list.szConnection); // release mem 3
        }
        if (optionCount > 1)
        {
            Marshal.FreeHGlobal(options[1].m_Value.m_StringPtr); // release mem 1
            if (optionCount > 2)
            {
                Marshal.FreeHGlobal(options[2].m_Value.m_StringPtr); // release mem 2
            }
        }
        Marshal.FreeCoTaskMem(optionsPtr); // release mem 4
        Marshal.FreeCoTaskMem(ipcoListPtr); // release mem 5
        if (returnvalue != 0)
        {
            // throw the error codes, they might be helpful
            throw new ApplicationException($"Set Internet Proxy failed with error code: {Marshal.GetLastWin32Error()}");
        }

        return true;
    }

    /// <summary>
    /// Retrieve list of connections including LAN and WAN to support PPPoE connection
    /// </summary>
    /// <returns>A list of RAS connection names. May be empty list if no dial up connection.</returns>
    /// <exception cref="ApplicationException">Error message with win32 error code</exception>
    private static IEnumerable<string> EnumerateRasEntries()
    {
        var entries = 0;
        // attempt to query with 1 entry buffer
        var rasEntryNames = new RASENTRYNAME[1];
        var bufferSize = Marshal.SizeOf(typeof(RASENTRYNAME));
        rasEntryNames[0].dwSize = Marshal.SizeOf(typeof(RASENTRYNAME));

View on GitHub (pinned to e01717d832)

Solutions

1. Run v2rayN as administrator when setting the system proxy.
2. Decode GetLastWin32Error (e.g. 'net helpmsg <code>') to identify the specific Win32 failure.
3. Close browsers/other proxy-managing apps that may lock WinInet settings and retry.
4. Ensure a network connection is active (WinInet refuses some options when no connection is up).
5. If running as a service/session 0, set the proxy from an interactive user session instead.

Example fix

// before
throw new ApplicationException($"Set Internet Proxy failed with error code: {Marshal.GetLastWin32Error()}");

// after - include the symbolic message for faster diagnosis
var code = Marshal.GetLastWin32Error();
throw new ApplicationException($"Set Internet Proxy failed (Win32 {code}): {new System.ComponentModel.Win32Exception(code).Message}");

// Best-effort pre-check: require admin and an active connection before setting proxy
if (!OperatingSystem.IsWindows()) throw new PlatformNotSupportedException();
// caller should ensure elevated session and an active network connection

static bool CanSetWindowsProxy() => OperatingSystem.IsWindows();

try
{
    ProxySettingWindows.SetProxy(/* ... */);
}
catch (ApplicationException ex) when (ex.Message.Contains("Set Internet Proxy failed"))
{
    var msg = new System.ComponentModel.Win32Exception(Marshal.GetLastWin32Error()).Message;
    _log?.Error($"WinInet set proxy failed: {msg}");
}

When it happens

Trigger: The proxy-setting routine builds an INTERNET_PER_CONN_OPTION_LIST, calls the WinInet set-option API, and returnvalue != 0 (the API reported failure). GetLastWin32Error yields the specific code (e.g. network unavailable, access denied).

Common situations: Running without administrator privileges on some Windows configurations; active/networked dial-up or VPN interfering with per-connection options; another process holds the WinInet settings lock; corrupt WinInet registry entries; calling on a non-interactive/session-0 context.

Related errors

• RasEnumEntries failed with error code: {result}

AI-assisted analysis of 2dust/v2rayN@e01717d832 (2026-08-13). Data as JSON: /api/errors/a4d7596a917305ac. Report an issue: GitHub.