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
After several minutes of being idle, WinSCP pops up with the following error:
Invalid access to memory
Behind that dialog is another dialog:
Invalid response to PWD command 'OPTS UTF8 command successful - UTF8 encoding now ON. '.
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.