Sound when the player connect and log in to server script.

[Lonsofore]

self playlocalsound("us_welcome.mp3"); //put your sound here

Here is your mistake - you should use soundaliases (.csv) files for sounds. You can find an example in iw_06.iwd. So, make your own .csv file in "soundaliases" folder, add there your sounds and then use them in your code with given name.