IIS FTP, Anonymous Login and DNS

I'm having a bazaar problem with my internet server. I'm using Smoothwall as my firewall/gateway and I have a w2k server running apache and IIS for a web server. Apache is for http and IIS is for FTP. Because I don't have a static IP address I use DirectUpdate to update my domain namewith my current IP address.

It's all been working great until all of a sudden I couldn't FTP using my domain name. At the time I was working on some PHP files and was FTPing back to the server to test. I can still get to the domain name using HTTP. I hadn't made any configuration changes when it happened.

FTP access still works when testing on the web server and I can still FTP using my current PPPo IP Address. But when using this IP I can't login Anonymously. Anonymous access is still enabled in IIS and the IUSR account looks fine.

The only thing I could think to try was rebooting Smoothwall and the Internet Server since the configuration hasn't changed since it was working. But it hasn't made any difference.

Does anyone have any ideas of what might be going wrong?

Well it seems their is a dns issue on my home network for the ftp access as I can ftp to the url name from work. And there is still an issue with anonymous login from work.