>Do you have any control over the secondary process? Can it be configured to wait XX seconds after seeing a new file appear, before it tries to copy it?

I believe using a .TMP and switching it with a rename at the end is better.

>If this is the root cause of the problem, why is it not happening with *all* the files you copy?

Because that is the only one subject to such monitoring for being handled somewhere else as soon as it exists.