After adding a FTP-connection to the list the problem was gone! Even after removing the FTP-entry, all SFTP connections seem to work flawlessly now. In my test before i had only SFTP connections.
I will try to reproduce the error and see if adding a FTP-server really is the key to get it working.

Hello! I have the same problem here (G1, cyan 4.0.4) with andftp version 1.0RC1 and 1.0 final. After reinstalling andftp or rebooting the phone i can connect exactly once to machine via SFTP, successive tries immediatly abort after touching the connect-button with a force-close message. I tried with...