7.0.3 is very old. In fact I don't think ioFTPD switched to OpenSSL until like v7.4. 7.7.3 should be much more stable than 7.0.3 was under load.
More importantly the microsoft encryption libraries used in v7.0.3 can't be upgraded by using the OpenSSL libs so if you want to use the new features you'll have to upgrade.
Not sure if it's easier to follow the upgrade directions for the releases between yours and the latest, or just use a file difference tool to see what changed and merged the files. Either way just make a copy of your current ioFTPD dir when the server isn't running so you'll have a fallback if you goof something up
