tidFTP problem

I recently converted from WinShoes to Indy 9, and on the whole have
got most things working.
I receive the following error when attempting an FTP put, but only on
one machine - another machine works correctly.  Both machines use MS
proxy client, and both are on the same network.  Other external socket
level communication works on both machines.

Currently using idFTP ver 9.00.10
Any ideas, or debugging techniques?  

Socket Error # 10056
Socket is already connected.

Last Cmd Result:"Opening BINARY mode data connection for
StockList.csv."