unsuccessful transfer => cached session permanently down

I use a VPN with my school machine, but need to turn it on and off during the day for other local networking purposes.

If I kill the VPN and try to transfer to school, the transfer obviously fails with:
Resolving host name 192.168.1.66...
Connecting to (192.168.1.66) -> IP: 192.168.1.66 PORT: 21
Connected to (192.168.1.66) -> Time = 0ms
Socket connected waiting for login sequence.
Connection closed.


However, after I reconnect the VPN, the server just times out when I try to transfer a file with the old cached session. I have to close the cached session and restart it before the program will allow me to transfer a file.