if(!isFile("Add-Ons/MyScript.cs"))
{
if($Server::Dedicated)
echo("MyScript is installed wrong. Redownload the mod and extract it to your main Blockland folder.");
else
schedule(1000,0,clientcmdmessageboxOK,"Error","MyScript is installed wrong. Redownload the mod and extract it to your main Blockland folder.");
return;
}
Change myScript for the actual filename of your script file, and put it at the top of the file.