"Operation not permitted" intermittently when adding source from SMB

If this is too much of a Kodi question, could someone pls suggest a forum?

This problem is really frustrating me. (See pic below)

In the loungeroom i run a LibreElec PC (using a usb stick).
But all the media is stored on a Windows XP PC in another room - with vids on several external hard drives.
(Yes, I know I 'shouldn't' run XP, but I have my reasons and its MOSTLY working).

I've successfully set up an SMB share, grabbing files from the Xp PC.
But SOMETIMES, when I'm trying to add a VIDEO SOURCE using FILES, it says 'Operation not Permitted' and won't open it.

(Videos > Files > Add videos > Browse > tap on the SMB share)

It's really frustrating because it happens 70% of the time.

Meanwhile all the vids that are already added, play just fine.

Sometimes I can get it to work if I SUSPEND and try again.

The LibreElec PC is plugged directly to the router with a blue cable.
That router also operates a wifi network which the source XP PC is connected to.
I also have a wifi-dongle in the LibreElec PC, because Im not sure if perhaps it needs it to get the files of the source XP computer.