In Windows 10 (64-bit, latest version of 4console.dll, and tcc.exe), I keep getting the following error message:

> seticon c:\Windows\Resources\icons\tcc_blk.ico
SETICON error: code = -4

> dir c:\Windows\Resources\icons\tcc_blk.ico
10.06.2009 07:56 13.262 tcc_blk.ico

the icon file is loaded though. The error does not appear in Windows 7. Any clues?
SetConsoleIcon is undocumented, so I have no documentation and its behavior may have changed. And I don't have Windows 10 to test on. After trying to get a handle (hIcon) to the icon you want, SETICON does this.
if ( hIcon != NULL )
       rv = -4;
       hOldIcon = GetConsoleIcon();
       if ( SetConsoleIcon(hIcon) )
           rv = 0;
So, apparently, it's succeeding (you said it works, right?) but returning FALSE
I still don't have Windows10 to test on. Is it the same problem as above ... working but giving an error message? If it does work, you could (temporarily) redirect the error message to NUL (2> NUL). I'll look at it this weekend but I'll be flying blind.
I put a new build of 4CONSOLE on I didn't change the logic in SETICON, so it may still succeed but say it didn't. But I did change the error handling, so we might get a more enlightening error message.