ftp connection problems

I've got a client who needs a piece of software to connect to a server via ftp.
I've configure ftp on the server in IIS.
the client connects to a root folder (that is the username of their account) and then needs to put the files directly into a particular folder.
It works for me but isn't working for the client's software
I can connect in two ways successfully:

1.in fireftp by giving it the ip w.x.y.z and the relevant username and password - this works fine and I go into the correct root folder.  I can also set the inital sub folder in fireftp and this works. I can transfer files perfectly.

2. in firefox by using the ip ftp://w.x.y.z/subfoldername
this asks me for the username and password and then goes straight into the subfolder. I can transfer files perfectly

However - the clients software needs to append the subfolder to the ip - e.g. w.x.y.z/rootfoldername/subfoldername. When it does this it says it connects ok (I can see the connection in the ftp log) but when it tries to transfer a file into the director it returns:

Error: coms_win080523b.jpg 200 Type set to I.  200 PORT command successful.  550 rootfoldername/subfoldername/coms_win080523b.jpg: The system cannot find the path specified.; Retrying ...

the entry in the ftp log says:

12:38:33 a.b.c.d [153]created rootfoldername/subfoldername/coms_win080523b.jpg 550 3
12:38:34 a.b.c.d [154]USER username331 0
12:38:34 a.b.c.d [154]PASS - 230 0
12:38:34 a.b.c.d [154]created rootfoldername/subfoldername/coms_win080523b.jpg 550 3

If I try and connect in fireftp by replacing the ip with w.x.y.z/rootfoldername/subfoldername w.x.y.x/subfoldername then it won't connect.

My feeling was that he's trying to get another folder too deep and that he shouldn't be putting the root - but he says he tried that and it was worse! What am I missing???? The connection is ok, the settings sound ok

What am I missing??
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Look at the privledges on the folder. Sounds like he doesn't have authenication.
uniteformAuthor Commented:
that was my first guess - but I've added full privileges for the user he's connecting as. The fact that I can transfer files into the folder using the same account details would also preclude this, wouldn't it?
I think it might be the underscores it doesn't like try that....
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uniteformAuthor Commented:
worked on the last box that was exaclty the same setup, and this is something I can't change (it's intrinsic to the application he's using)
any other ideas?
Did you check the firewall to see if it allowing it to transfer? What port is it trying to transfer from? Do you have it on a domain behind a firewall? Even if it's in the DMZ zone then you still need authenication from the domain controllers.. If it is the software it would be easier to download another FTP program.

You can download core FTP from http://www.coreftp.com/download.html it's a free FTP tranfer program.
uniteformAuthor Commented:
it's none of the above,I"d already checked the firewall etc and as I could connect myself and transfer files using exactly the same details then it couldn't be that. - I managed to get him to let me look at the software application itself (it has a built in ftp client) and play around with it and there seems to be a fault with the application itself.  I've now got it sending via another route so problem solved. thanks for your help anyway
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