The issue in my instance was due to Windows 10 Controlled Folder Access.
Screen snip here showing relevant log entry:
To view Protection History
Follow these steps to identify if you have a matching Protection History entry to the one I have shown above.
- Press the Start button.
- Type controlled folder access, press Enter.
- You should the Ransomware Protection window appear, example: https://imgur.com/a/zJan0Di
- From this window, click block history
- The Protection History window will open, the relevant entry will likely be the most recent at the top.
From the relevant entry in the Protection History window, select "Actions: Allow on device" and then attempt the SD Card write again.
if this is the cause of your issue, the write should succeed.