G'day again Leo. Thanks for your detailed reply. I've commented on your thoughts.
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It won't be due to Windows 10, at least unless you are using a very old version of Opus. Windows 10 is what almost all of us are using. (That said, Windows 10 can install some poor drivers by default, see below.)
OK - no conspiracy theory, then.
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Try using the Copy Files button rather than drag & drop to see if that makes a difference.In other words, get the folder you want to copy from in the left file display, and the one you want to copy to in the right. Then select some files to copy in the left, and click Copy Files.
No ... copy & paste won't work either. -
Are you running Opus elevated as administrator? The admin account/context may see drives differently to the standard one, which could cause problems.If you are doing that: Instead of that, use the UAC support built in to Opus instead of elevating the whole program. See: Why NOT to run Opus as Administrator under UAC .
At the moment while I'm setting everything up I'm using the Admin account in Win10. Is that what you are asking?
- Which Opus version are you using?
DO10.0
Your profile says 10, which is very old now, but if you're using 11 or 12, what is this setting in Opus set to?
- Preferences / Miscellaneous / Advanced [Filesystem]: copy_nonbufferio_thresholdTry setting it to 0 (zero) if it isn't already. Other settings can cause trouble with some things which don't work correctly with non-buffered I/O.
Found in DO10. Was 1MB; now set to zero - no change to copy problem
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You could generate a Process Monitor log of what happens to see if that shines any light on what's going on:Process Monitor instructions
Will look into that. -
Make sure your drivers are up to date. Windows 10 can install some poor driver choices by default. The important ones for file copying are the ones that usually come from the device manufacturer's website for that device (or motherboard on custom-made PCs), in the downloads area: The motherboard/chipset drivers and the SATA drives.
(maybe) Easus corrupted or overwrote driver files. It was the only program installed since everything worked. Something changed - DO10 used to work perfectly. When restored back a few days the computer and DO work perfectly until I re-boot (which I assume re-loads corrupted drivers?).
Will download and install latest Intel drivers to see if that works. Most reluctant to do BIOS at this stage.(Have memories of doing BIOS updated from 25 years ago and the long nervous wait to see if the motherboard got bricked.)
- Other than that, there isn't really any reason Opus shouldn't be able to access the same drives that Explorer does.
And that's the problem - DO10 will now NOT do what Windows Explorer can do - ie successfully copy files across drives. BUT it used to.
If (and I'm in serious lack-of-knowledge area here) DO operates in a 'shell' as does Open Office? (which also throws up weird writing errors) does that tell you anything not already considered?
The reason for getting a screen shot into this thread is to show the rather weird directory tree in DO.
In words:
The tree is set to start at
"Drives". Then under that is
D:\ (NUC Data) with a cube icon, then
C:\ (OS Win 10) then
D:\ (NUC Data) but with a standard drive icon then
E:\ (Lumix) [My camera's SD card via a USB adaptor] then
T:\ (NUC Backup) [My daily back-up drive]
Why there is a D:\ listing before the C:\ listing has me stumped.
BOTH of the D:\ (NUC DATA) listings are fully functional - I can scroll down and view and manipulate an image, for instance, but can't save back to exactly the same drive the original image was derived from.
[SIGH] OK - doing drivers tomorrow. If that doesn't work a Win 10 repair then [shudder] BIOS update.
Thanks for all your help so far, Leo. It is appreciated.
It's my tired old brain that's having trouble soaking up all that info. 
Regards.