Invalid access to memory

WinSCP 4.3.2 (Build 1201)
Problem has always occurred, in at least previous two versions
Protocol: FTP, No encryption, port 21
GUI: Yes (haven't tried scripting/automation), commander style
Server software: Microsoft IIS 7

Problem:

After several minutes of being idle, WinSCP pops up with the following error:


Behind that dialog is another dialog:


WinSCP subsequently tries to reconnect, but simply hangs on a white (empty) reconnection dialog.

If there's any further diagnostics that I can do for you, please let me know as I can reproduce this every time.

Disabling passive mode appears to cause WinSCP to hang without any error messages or reconnection dialog at all.

In either case (passive mode on/off), when the application hangs, the only thread showing any signs of life is cycling around the following function call:

Correction on my previous post: I had disabled Keep-Alive, not passive mode. I am presently testing with both disabled.

With Keep-Alive and passive mode disabled, WinSCP 4.3.2 hangs as well.

I have sent you an email.