GnuTLS error -53: Error in the push function
With firewalls disabled and off I still got the problem.
I Googled the error:"GnuTLS error -53: Error in the push function" and found a discussion thread on a FileZilla forum about a confirmed bug in gnuTLS. (I've have a different Linux kernel level 2.6.4 than the instructions on howtoforge.com). My gnuTLS is gnutls-2.10.5-1.fc15.x86_64 while my FileZilla agent uses 2.10.4.
So I downloaded a different FTP client and now everything works as it should.