File and/or Directory not found - it's right there though??

Hi,
Sincere apologies if this is covered elsewhere - my search produced no relevant results.
Recently my uploads (but not downloads) have been starting up for twenty seconds or so and then halting claiming that "File and/or Directory not found". This makes no sense as I can quite clearly see the files exactly where I told Smart FTP they were. I right-click on the upload, choose properties and reselect the source file to no avail - same thing happens again.
Has anyone got any ideas?

For the record I'm using XP SP2 with a McAfee firewall set to grant Smart FTP 1.1.985 full access to the web. I had been having a problem whereby my whole AOL broadband connection would fall off if Smart FTP was *only* uploading - it didn't seem to happen if there was at least one download going on at the same time - since then I've had both up and downloads in my global queue to avoid this and it all seemed to be working.... until this. Many thanks for your time and attention. Congratulations for producing an otherwise excellent FTP client.