Hi John,
I guess you config will look like this:
static (inside,outside) netmask 255.255.255.255
access-list outside permit tcp any host eq 21 (or ftp)
access-group outside in interface outside
When you got the wrong password message, do you see any login attempt/process failed in your FTP server?
If YES, then the FTP request is successfully reached your FTP server -> need to check your server then.
If NO, then it might be the firewall who intercepted and tried to authenticate your ftp access/request.
BTW, do you have authentication proxy parameter in your config, something like "aaa authentication match" (not the aaa authentication http}telnet...).
Rgds,
AK