I have several users complaining that they can't connect to our site with older browsers (Netscape 3x). I tried Netscape 3.0 and I get a message-box from Netscape saying "The security library has experienced a database error. You probably will not be able to connect to this site securely." What do I do now?

These old browsers have an old Thawte root certificate in them. You probably have a newer Thawte certificate. There are instructions on the Thawte website for upgrading these old browsers to work with the new Thawte root certificate. See SSL Certificate Overview: 3.x Root Rollover.