In the link which you provided I noted it took me to AOL's email troubleshooting site. Is AOL your ISP? Did you try the suggestions on their troublshooting site?
Regarding the messesages you cannot retrieve from your Inbox, see if "Compacting" the emails helps. It's been awhile but, to do this, open up Netscape's email>File>Compact. Hopefully, a knowledgeable user who is still using Netscape v7.0.2 will correct me if I am wrong.
Suggest that you also check out Netscape's Mail Help. There is a lot of useful info in there.
This link may be of some help also:
http://switch.sillydog.org/howtoswitch.php
You might also try rebuilding your desktop.
http://docs.info.apple.com/article.html?artnum=10182 Rebuilding Desktop File and Icon Recovery.