vsftpd + valid ssl cert - client says unknow cert :(

[Joffer]

I've got vsftpd up and running, almost everything is working flawlessly as I want it:
- virtual users in mysql
- locked virtual user into their own jailed home folder
- ssl encrypton

SSL encryption/auth works fine, except for one thing, my ftpclient (filezilla) complaines about an "unknown certificate", see image here:

http://img259.imageshack.us/img259/6...carrotnji1.jpg

I created my private key and a csr from that which I used to buy a SSL123 certificate from Thawte. When I got it, I 'cat' them together into a .pem file and pointet to it in vsftpd.conf (it is an rsa key btw). If I say 'accept' to the "unknown" certificate everything works fine, but I really want it to NOT show (the warning). It's going to be a live server at work, so I need it to be professional without this warning message.

I'm quite frustrated now. I've googled my eyes out and have not found one example of vsftpd used with valid certificates, only self signed. Most articles/wikis/guides/howtos just say something like ".. or you can buy a valid certificate at places like VeriSign or Thawte".