Here's the reason.
I use a service called Dropbox (
https://www.getdropbox.com/home). It includes an online storage area and a desktop program that synchs files between both areas.
I use my dropbox on both my desktop computer and my netbook machine. When I close URP4 on my desktop, the files I worked on are immediately uploaded to the online dropbox and my netbook downloads them to its own iteration of the dropbox folder.
The folders are on different letter drives (desktop L and netbook C). Thus the data file locations are inherently different and external files that are referenced within URP4 can be resolved only via relative referencing - relative to the main URP4 data file.
Since URP4 on my desktop "wants" to create the external files inside a non-existent-newly-created mozybackup folder, and since my netbook has no way of "understanding" this, the external files that are created in a Ctrl+J operation can't synch up.
The only way for me to synch them is to create them first in, say, Open Office and to then import those files into UPR4. This works, but it is immensely more cumbersome than creating the item in URP4 and doing a Ctrl+J operation when it's called for.
Hopefully this is clearer than mud.
Let me know if not.
Regards,
Bal