Connection timeout at login for one user

[WarrenHead]

Hey,

I have one user who cannot get into my ftp server. He can login by giving his username and password, and go into passive mode, but then his connection just sits there. He does not receive a directory listing, so cannot continue and is logged out after the connection timeout setting for not doing anything.
His pc is very remote, so I cannot see for myself what this person is doing, but he can get into other ftp servers he claims, so I'm at a loss where to search for clues, as is he.

Thanks in advance,