lammert - 10:50 am on Aug 10, 2010 (gmt 0)
The last line 550 Access is denied. error is generated by the FTP server you are connecting to. It therefore looks like the server is blocking the access, rather than something in the network or the client.
It may be that after an upgrade of the server software or server configuration the FTP server is confused by the absolute path as the destination. You could therefore try
put c:/file.php file.php
Another thing to check is the access rights of the destination file and directory. If the file already exists and you don't have write permission to that file, an access denied error may also occur.