function serverCmdMap(%client, %name)
{
messageClient(%client, '', "<bitmap:/images/map.png>");
}
You were missing the quotations for the actual message argument, which is the bitmap, and also missing a closing bracket for the function. Keep in mind that this will look for <blockland-directory>/images/map.png, so if you don't have the images folder or the map.png image, it will spew a bunch of errors in the console.
Also keep in mind that messageClient is for chat messages, so the map image will appear in the chat. If you wanted it to appear in the center, you could use %client.centerPrint(%message, %time);