I was setting up and testing my ProFTP on a new server as I stated in this guide:
After testing I got this error in Filezilla:
GnuTLS error -53: Error in the push function
After much reading and testing I can safely say that this is a firewall issue.
Just follow my How to: CentOS Virtualmin secure ProFTPD guide to the dot and you should be fine.
Make sure that you have set the passive port for ProFTPD and that you have opened these in the firewall