FLASHFXP 500 I won't open a connection to [my internal IP

Hi, I am having troubles accessing via FTP. I am under a corporate firewall, so when I am connecting with FileZilla it says:
500 I won't open a connection to [my internal IP] (only to [external IP])
You can try few things...

a)Try to use passive mode>> click Edit -> Settings… -> connections -> Firewall settings, check "Passive Mode".
b) Check if your corporate firewall has port 21 opened.
c) Try using explorer ftp by typing below URL in an Internet explorer window
ftp://username:password@frihost.net
of course swap username and password with your real user name and password and see if it works.