[Cefoxtrot]

This just started: When I try to open or convert a MOBI formatted book, I get the following error:
calibre, version 1.12.0
ERROR: Could not open ebook: unpack requires a string argument of length 2

Traceback (most recent call last):
File "site-packages\calibre\gui2\viewer\main.py", line 40, in run
File "threading.py", line 761, in run
File "site-packages\calibre\ebooks\oeb\iterator\book.py", line 99, in __enter__
File "site-packages\calibre\customize\conversion.py", line 241, in __call__
File "site-packages\calibre\ebooks\conversion\plugins\mobi_in put.py", line 33, in convert
File "site-packages\calibre\ebooks\mobi\reader\mobi6.py", line 79, in __init__
error: unpack requires a string argument of length 2
================
I tried to repair and reinstall Calibre, but the errors persist. Is this a know issue? Is there a fix?
Thank you.