[MontyJ]

Originally Posted by kovidgoyal

It sounds like the catalog thumbnail cache file is corrupted. Try posting the full error message by clicking show details on the error message, that way we can be sure.

Thanks Kovid. Here is the full error msg:
calibre, version 1.27.0 (win32, isfrozen: True)
Conversion Error: Failed: Generate catalog

Spoiler:

Generate catalog
Sections: Authors, Titles, Series, Genres, Descriptions
Catalog_EPUB_MOBI('Calibre Master Fiction'): Generating mobi for default in GUI environment, locale: 'English'
connected_device: 'None'
book count: 12246
opts:
author_clip: 100
catalog_title: u'TechSoB - NonFiction'
connected_kindle: False
creator: u'Monday, March 10, 2014'
cross_reference_authors: True
description_clip: 380
exclude_genre: u'\\[.+\\]|^\\+$'
exclusion_rules: ()
fmt: u'mobi'
genre_source_field: u'Tags'
header_note_source_field: ''
merge_comments_rule: '::True'
output_profile: 'default'
prefix_rules: ()
search_text: None
sort_by: None
sort_descriptions_by_author: True
sync: False
thumb_width: u'2.00'
use_existing_cover: True
Begin catalog source generation (0:00:00)
93 enabled genres:
Action, Adolescence, Adult, Adventure, Africa, African American, American,
Anthologies, Anthology, Art, Chase, Childrens, Christian, Christianity,
Classics, Comics, Coming of Age, Contemporary, Contemporary Fiction,
Contemporary Women, Crime, Detective, Domestic Fiction, Domestic Life,
Drama, Epic, Espionage, Essays, European Literature, Fairy Tales, Family Life,
Family Saga, Fantasy, Fiction, France, Franco-Prussian War, General,
Genre Fiction, Ghost, Greek mythology, Historical, History, Horror,
Humanities, Humor, Humorous, Humour, Inspirational, Juvenile, Literary,
Literary Collections, Literary Criticism, Literary Fiction, Literature,
Medical, Military, Modern, Music, Mystery, Occult, Paranormal, Parodies,
Philosophy, Poetry, Politics, Private Investigators, Prose, Psychological,
Regency, Religion, Religious, Romance, Romantic, Sagas, Satire, Serial Killers,
Short Stories, Social Issues, Speculative Fiction, Spirituality, Suspense,
Thriller, Thrillers, Trains, True Crime, United States, Urban, War,
Western, Westerns, Women, Women's Fiction, Young Adult
0 excluded genres:

Custom fields:
#formats 'Formats' composite
Thumbnails:
DPI = 100; thumbnail dimensions: 200 x 266
existing thumb cache at C:\Users\Slick\AppData\Local\calibre-cache\catalog\thumbs.zip, cached_thumb_width: 2.00"
Sorting titles (0:01:02)
Sorting database (0:01:02)
Thumbnails (0:01:04)
unhandled exception in catalog generator
Python function terminated unexpectedly
File name in directory "72c9dc43-8073-49f4-89d-4c15-a8e9-b45c669d301f-0" and header "72c9dc43-8073-49f4-89df-be4d07f60082-0x71157126" differ. (Error Code: 1)
Traceback (most recent call last):
File "site.py", line 132, in main
File "site.py", line 109, in run_entry_point
File "site-packages\calibre\utils\ipc\worker.py", line 195, in main
File "site-packages\calibre\gui2\convert\gui_conversion.py", line 68, in gui_catalog
File "site-packages\calibre\library\catalogs\epub_mobi.py", line 405, in run
File "site-packages\calibre\library\catalogs\epub_mobi_builde r.py", line 275, in build_sources
File "site-packages\calibre\library\catalogs\epub_mobi_builde r.py", line 4395, in generate_thumbnails
File "site-packages\calibre\utils\zipfile.py", line 760, in __init__
File "site-packages\calibre\utils\zipfile.py", line 877, in _calculate_file_offsets
RuntimeError: File name in directory "72c9dc43-8073-49f4-89d-4c15-a8e9-b45c669d301f-0" and header "72c9dc43-8073-49f4-89df-be4d07f60082-0x71157126" differ.