Update: After I turned off the passive mode (on the FTP client) and use the active mode, it seems to be working now. Does anyone know the technical side of why this would happen?

I'm having the same issue with FTP. Did some searching and found this page about load balancing routers and FTP (PASV mode) http://www.ncftp.com/ncftpd/doc/misc/ftp_and_firewalls.html#PASVLBProblems...