Conversion not working in calbre GUI -- CLI OK

Help. I must have done something very bad.

Calibre was working fine -- I even added plugins and it did everything
as advertised. Then I did something; I'm not sure what, but I did run ccleaner
and Spybot Search and Destroy.

Now it won't do conversions using the GUI -- but it will do it in command line mode!
When I click on the icon for Convert Books, either individually or bulk,
or in Preferences/Convert, it just comes back with an error message:

ERROR: Unhandled exception
TypeError: expected string without null bytes


I tried uninstalling calibre and re-installing with a new download. To no avail.
I tried creating a new library. Same error.

I even tried it in safe mode. Didn't help.


I have Windows 7 (32/64 running in 32bit mode).
Here is the debug log:


calibre Debug log
calibre 1.22 isfrozen: True is64bit: False
Windows-7-6.1.7601-SP1 Windows ('32bit', 'WindowsPE')
32bit process running on 64bit windows
('Windows', '7', '6.1.7601')
Python 2.7.5
Windows: ('7', '6.1.7601', 'SP1', 'Multiprocessor Free')
Traceback (most recent call last):
File "site-packages\calibre\utils\config.py", line 289, in refresh
File "site-packages\calibre\utils\config.py", line 378, in raw_to_object
File "encodings\utf_8.py", line 16, in decode
UnicodeDecodeError: 'utf8' codec can't decode byte 0x84 in position 240: invalid start byte
Starting up...
Started up in 27.91 seconds with 1 books
calibre 1.22 isfrozen: True is64bit: False
Windows-7-6.1.7601-SP1 Windows ('32bit', 'WindowsPE')
32bit process running on 64bit windows
('Windows', '7', '6.1.7601')
Python 2.7.5
Windows: ('7', '6.1.7601', 'SP1', 'Multiprocessor Free')
Traceback (most recent call last):
File "site-packages\calibre\gui2\actions\convert.py", line 156, in convert_ebook
File "site-packages\calibre\gui2\actions\convert.py", line 173, in do_convert
File "site-packages\calibre\gui2\tools.py", line 41, in convert_single_ebook
File "site-packages\calibre\gui2\convert\single.py", line 151, in __init__
File "site-packages\calibre\gui2\convert\single.py", line 206, in setup_pipeline
File "site-packages\calibre\gui2\convert\single.py", line 204, in widget_factory
File "site-packages\calibre\gui2\convert\metadata.py", line 61, in __init__
File "site-packages\calibre\gui2\convert\__init__.py", line 73, in initialize_options
File "site-packages\calibre\ebooks\conversion\config.py", line 40, in load_defaults
File "site-packages\calibre\ebooks\conversion\config.py", line 80, in from_string
TypeError: expected string without null bytes