Inside clients can't list or browse FTP sites behind Cisco ASA Pix

The fix to this issue is to get into config mode and issue the following command..
fixup protocol ftp 21

Port address translation and PPTP pass through

If you are configure a Cisco Pix or ASA device and you have a server on the inside interface and clients on the outside who are using PPTP to VPN into the network you must make sure you do the following things.
Allow GRE traffic in the security policy
Allow PPTP traffic in the security policy
static entry for pptp on 1723 to your server
run this command in configure mode “fixup protocol pptp 1723”