[FONT=&]This evening I was once again searching for advice on the problem and came across this thread, [/FONT][FONT=&]https://answers.microsoft.com/en-us/msoffice/forum/msoffice_word-mso_other-mso_2010/adding-a-mapped-network-drive-to-the-office-2010/ef12d2c6-4b55-42fe-b28c-527d8da6d6fb[/FONT]
[FONT=&]And although this didn't directly solve the problem, I was able to follow one of the suggestions in that thread [launch Access using "run as Administrator"] and I rather fell through this to the solution.[/FONT]
[FONT=&]When I had been manually entering the path to the network folder in my Trusted Locations field, I had been using a path name that was configured in exactly the way that Microsoft Windows Explorer "sees" the folder. That is to say that the path name appears as:-[/FONT]
[FONT=&]"T:\Data\Office Files\Microsoft Access"[/FONT]
[FONT=&]Where T: is my assigned drive letter, and this is in turn mapped [in Windows Explorer] as "\\192.168.1.42\Public"[/FONT]
[FONT=&]Now, the interesting thing here is that the "Public" suffix [which is the way that QNAP "presents" or "exposes" the named share that it is hosting, is actually truncated by Windows Explorer, invisibly. So what you end up seeing, once you've made that initial map, is as I represented it above - i.e. "T:\Data\..."[/FONT]
[FONT=&]OK, I bet you can see where this is going...[/FONT]
[FONT=&]I went back in to Trust Center, to Trusted Locations, to my existing mapped entry for this network share... I changed the entry from this:-[/FONT]
[FONT=&]\\TS670\Data\[/FONT]
[FONT=&]to this[/FONT]
[FONT=&]\\TS670\Public\Data\[/FONT]
[FONT=&]and, hey presto, everything now works... As a sort-of extra tip, I mention that I "fell through" to this solution - and this is because what I was actually able to do this time around was:-[/FONT]
[FONT=&]1. Run Access as Administrator[/FONT]
[FONT=&]2. Open Trust Center[/FONT]
[FONT=&]3. Select "Trusted Locations"[/FONT]
[FONT=&]4. Single-Click my "User Location" entry for the NAS box, then click "Modify..."[/FONT]
[FONT=&]5. Ignore the "Path" value, even though it is possible to hand-hack it here, and instead click "Browse"...[/FONT]
[FONT=&]6. Realise that, as Administrator, I can no longer "see" my 2 QNAP network drives [which I map as Q: and T:], presumably because that mapping is done under my default, non-Administrator ID, and I am currently running Access as "Administrator" ...[/FONT]
[FONT=&]7. Instead go to "Network"[/FONT]
[FONT=&]8. Double-click the "server" icon for the relevant NAS box...[/FONT]
[FONT=&]9. Find the 5 shares that I have configured on the NAS, and pick the relevant one...[/FONT]
[FONT=&]10. Pick the "Data" folder within that network share, to at least put *some* limitations on the extent of the trust...[/FONT]
[FONT=&]11. Save and quit access[/FONT]
[FONT=&]12. Re-launch access as a non-Administrator user, and observe that I get full access to the file, without the annoying warning...[/FONT]
[FONT=&]This is, I hope you'll agree, a pretty convoluted set of steps. It is made all the more interesting/frustrating/difficult by virtue of the fact that when mapping directly to the NAS via Windows Explorer, something in the way that Explorer "displays" that network drive actually suppresses the "Public" part of the network share.[/FONT]
[FONT=&]In this instance, my familiarity with Windows and my willingness to simply jump into the text box and manually enter the pathname was actually the cause of the process failing to map.[/FONT]
[FONT=&]However, I will not accept that as the problem here. Rather, the actual problem is the completely useless error message issues by Access, which suggests that the issue is a security problem and not because it can't find the folder. I suspect but don't know that the programmer who coded the error condition presumed that if they were unable to find a folder as entered, it was because they did not have permission to view it - and so defined the error accordingly.[/FONT]
[FONT=&]However, bottom line is - this now works.[/FONT]
[FONT=&]I do hope that anyone else who hits this is going to be able to find and follow this explanation of the fix.[/FONT]