[lburg801]

PC laptop, Win7, no portable device, Adobe Digital Editions.
When I try to add a cover (download or file on computer or copy/paste), the image shows but when I click OK, I get this error msg.

calibre, version 3.20.0
ERROR: Permission denied: Could not change the on disk location of this book. Is it open in another program?

Locked file: C:\Users\T_H_M\Documents\Calibre Library\Roald Dahl\George's Marvellous Medicine (23)\cover.jpg

Traceback (most recent call last):
File "site-packages\calibre\gui2\metadata\single.py", line 579, in apply_changes
File "site-packages\calibre\gui2\metadata\basic_widgets.py", line 1210, in commit
File "site-packages\calibre\db\legacy.py", line 713, in set_cover
File "site-packages\calibre\db\cache.py", line 63, in call_func_with_lock
File "site-packages\calibre\db\cache.py", line 1230, in set_cover
File "site-packages\calibre\db\backend.py", line 1427, in set_cover
File "site-packages\calibre\utils\img.py", line 221, in save_cover_data_to
File "site-packages\calibre\startup.py", line 116, in local_open
IOError: [Errno 13] Permission denied: u"C:\\Users\\T_H_M\\Documents\\Calibre Library\\Roald Dahl\\George's Marvellous Medicine (23)\\cover.jpg"

The file is not being used by another program. I have shut everything down but Caliber. It makes no difference. I have done an uninstall and reinstall and even cleaned the registry as a last resort. I'm stumped.