A few things to try.
1. While testing, they only need to use /nick to change from-then-to the nick. They don't need to actually connect/disconnect from that network. It won't respond to yourself changing nick.
2. Does it display a message that they're here/gone, and just the sound doesn't play? If not, either verify that the notify tab of address book has "enabled" checked, or type: /notify on
3a. See if problem continues when you disable scripts: /remote off
3b. Be sure to turn back on. /remote on.
4. Verify mirc-options/sounds has the box checked "enable sounds"
5. Make sure it lists the nick here: /notify -l
6. Paste this command:
//var %i $notify(0) | while (%i) { echo -a %i $notify(%i) ison: $notify(%i).ison network: $notify(%i).network $notify(%i).offline $notify(%i).sound | dec %i }
It should correctly report if that nick is here/away. The network should either be blank, or be the correct $network string for that network. (Usually shown in the titlebar of status window or type //echo -a $network ). It should list the path to the sound file.
If it lists the path\filename for a sound, highlight it to paste as the parameter to the /splay command, and you should hear the sound.
If it doesn't list the sound, either you didn't put it into the correct entry in the 'notify' tab, or you put it as offline instead of online.
Edit: If they are online using that nick, this should also trigger the sound without needing a nick change: /notify
