Incorrect padding - Wrong key

[Daythril]

DeDRM isn't working on a book I just bought. Here's some text from the Calbre log:

ApplicationPaletteChange event ignored
Using calibre Qt style: True
ApplicationPaletteChange event received
calibre Debug log
calibre 6.8 embedded-python: True
Windows-10-10.0.19045-SP0 Windows ('64bit', 'WindowsPE')
('Windows', '10', '10.0.19045')
Python 3.10.1
Windows: ('10', '10.0.19045', 'SP0', 'Multiprocessor Free')
Interface language: None
Successfully initialized third party plugins: Gather KFX-ZIP (from KFX Input) (1, 49, 0) && DeDRM (10, 0, 3) && Package KFX (from KFX Input) (1, 49, 0) && KFX metadata reader (from KFX Input) (1, 49, 0) && KFX Input (1, 49, 0) && Set KFX metadata (from KFX Output) (1, 64, 0) && KFX Output (1, 64, 0) && Kindle Collections (1, 7, 29)
calibre 6.8 embedded-python: True
Windows-10-10.0.19045-SP0 Windows ('64bit', 'WindowsPE')
('Windows', '10', '10.0.19045')
Python 3.10.1
Windows: ('10', '10.0.19045', 'SP0', 'Multiprocessor Free')
Interface language: None
Successfully initialized third party plugins: Gather KFX-ZIP (from KFX Input) (1, 49, 0) && DeDRM (10, 0, 3) && Package KFX (from KFX Input) (1, 49, 0) && KFX metadata reader (from KFX Input) (1, 49, 0) && KFX Input (1, 49, 0) && Set KFX metadata (from KFX Output) (1, 64, 0) && KFX Output (1, 64, 0) && Kindle Collections (1, 7, 29)

The problem seems to be here:

Decrypting KFX DRM voucher: voucher
Traceback (most recent call last):
File "C:\Users\berkowitzm\AppData\Roaming\calibre\plugins\DeDRM.zip\kfxdedrm.py", line 105, in decrypt_voucher
File "C:\Users\berkowitzm\AppData\Roaming\calibre\plugins\DeDRM.zip\ion.py", line 886, in decryptvoucher
File "C:\Users\berkowitzm\AppData\Roaming\calibre\plugins\DeDRM.zip\ion.py", line 762, in pkcs7unpad
File "C:\Users\berkowitzm\AppData\Roaming\calibre\plugins\DeDRM.zip\ion.py", line 102, in _assert
Exception: Incorrect padding - Wrong key

The key is the same one I've been using forever; it has worked in the past.

Any ideas?

[ElleKayEm]

Looks like the newer KFX which cannot be decrypted. Guessing Kindle for PC updated on you. See this post for methods of getting books that can be decrypted and for preventing updates: https://www.mobileread.com/forums/showthread.php?t=283371