For a recent project I created several sets of Windows scheduled tasks that generate iCal files and FTP them to another server. Each file-generator task executes an ASP script that creates the customized iCal file. Then the corresponding FTP task runs a a batch file (.bat) that contains the commands to transfer the file.
After a while, I noticed that one of the iCal files was not being tranferred. Each iCal file has its own FTP task, so I compared one that was working to one that was not.
It turned out to be a permissions issue: for some reason the two scheduled tasks were assigned the permissions of different Windows users with slightly different privileges. The one that was working had full administrator privileges, where the user on the one that was not running had slightly lower privileges. One other thing to check: the Windows user that owns the scheduled task that executes the FTP batch file must be given Full Control permissions on that batch file.