>Probably stuck on discovering the source of the problem without it :-{
>
>Does the .tmp file renaming approach work ? If the second program attempts to copy that whilst it's still .tmp then you're back where you started......

The TMP file approach works at the testing phase. We would need to run it for a few months to be sure the problem went away. But, I cannot see how the same problem would come back. The reason is that the second program requires a specific extension before detecting and copying the file. Thus, for as long as .TMP exists, it will not be processed by another program. And, the rename command would only make that file available to the proper name once executed.