Ah, ok. Often, when some accounts do work & one doesn't, it's a port issue.

Go into your Dad's account & find his gnutella.net file, Hover the cursor over that file - how big is the file?
The thread below has a section about deleting/replacing gnutella.net - that will explain to you where the file is & how to find it: If LW Will Not Connect

Also, try deleting LW's preferences folder in your Dad's account - the help thread has detailed instructions for that.

Feel free to try any fixes in that help thread as well! If you're still stuck, please could you post back with your system details? The help thread has a link with info about the details that we need (bottom of thread)