I've been using Calibre almost since the start and it's a great piece of software. Strangely, recently I have been encountered conversion problems from EPUB to AZW3 and MOBI. In the spoiler you can find the error log. The KeyError is defined as u'cover.jpeg'.
Spoiler:
Konvertera bok 1 av 1 (Det svenska)
C:\Program Files (x86)\Calibre2\pylib.zip\dateutil\parser.py:339: UnicodeWarning: Unicode equal comparison failed to convert both arguments to Unicode - interpreting them as being unequal
Resolved conversion options
calibre version: 2.78.0
{'asciiize': False,
'author_sort': None,
'authors': None,
'base_font_size': 0.0,
'book_producer': None,
'change_justification': u'original',
'chapter': u"//*[((name()='h1' or name()='h2') and re:test(., '\\s*((chapter|book|section|part)\\s+)|((prolog|pr ologue|epilogue)(\\s+|$))', 'i')) or @class = 'chapter']",
'chapter_mark': u'pagebreak',
'comments': None,
'cover': u'C:\\Users\\ALKASA~1\\AppData\\Local\\Temp\\calib re_5f6yjk\\cpeejs.jpeg',
'debug_pipeline': None,
'dehyphenate': True,
'delete_blank_paragraphs': True,
'disable_font_rescaling': False,
'dont_compress': False,
'duplicate_links_in_toc': False,
'embed_all_fonts': False,
'embed_font_family': None,
'enable_heuristics': False,
'expand_css': False,
'extra_css': None,
'extract_to': None,
'filter_css': u'',
'fix_indents': True,
'font_size_mapping': None,
'format_scene_breaks': True,
'html_unwrap_factor': 0.4,
'input_encoding': None,
'input_profile': <calibre.customize.profiles.InputProfile object at 0x03B31A70>,
'insert_blank_line': False,
'insert_blank_line_size': 0.5,
'insert_metadata': False,
'isbn': None,
'italicize_common_cases': True,
'keep_ligatures': False,
'language': None,
'level1_toc': None,
'level2_toc': None,
'level3_toc': None,
'line_height': 0.0,
'linearize_tables': False,
'margin_bottom': 5.0,
'margin_left': 5.0,
'margin_right': 5.0,
'margin_top': 5.0,
'markup_chapter_headings': True,
'max_toc_links': 50,
'minimum_line_height': 120.0,
'mobi_toc_at_start': False,
'no_chapters_in_toc': False,
'no_inline_navbars': False,
'no_inline_toc': True,
'output_profile': <calibre.customize.profiles.KindlePaperWhiteOutp ut object at 0x03B31E30>,
'page_breaks_before': u'/',
'prefer_author_sort': False,
'prefer_metadata_cover': False,
'pretty_print': False,
'pubdate': None,
'publisher': None,
'rating': None,
'read_metadata_from_opf': u'C:\\Users\\ALKASA~1\\AppData\\Local\\Temp\\calib re_5f6yjk\\s6rvqx.opf',
'remove_fake_margins': True,
'remove_first_image': True,
'remove_paragraph_spacing': False,
'remove_paragraph_spacing_indent_size': 1.5,
'renumber_headings': True,
'replace_scene_breaks': u'',
'search_replace': '[]',
'series': None,
'series_index': None,
'share_not_sync': False,
'smarten_punctuation': False,
'sr1_replace': None,
'sr1_search': None,
'sr2_replace': None,
'sr2_search': None,
'sr3_replace': None,
'sr3_search': None,
'start_reading_at': None,
'subset_embedded_fonts': False,
'tags': None,
'timestamp': None,
'title': None,
'title_sort': None,
'toc_filter': None,
'toc_threshold': 6,
'toc_title': None,
'transform_css_rules': '[]',
'unsmarten_punctuation': False,
'unwrap_lines': True,
'use_auto_toc': False,
'verbose': 2}
InputFormatPlugin: EPUB Input running
on C:\Users\ALKASA~1\AppData\Local\Temp\calibre_5f6yj k\sdf4kq.epub
Parsing all content...
Parsing OPS/xhtml/27_chapter27.xhtml ...
Parsing OPS/xhtml/36_chapter36.xhtml ...
Parsing OPS/xhtml/28_chapter28.xhtml ...
Parsing OPS/xhtml/29_chapter29.xhtml ...
Parsing OPS/xhtml/37_chapter37.xhtml ...
Parsing OPS/xhtml/30_chapter30.xhtml ...
Parsing OPS/xhtml/31_chapter31.xhtml ...
Parsing OPS/xhtml/38_chapter38.xhtml ...
Parsing OPS/xhtml/32_chapter32.xhtml ...
Parsing OPS/xhtml/tack.xhtml ...
Parsing OPS/xhtml/back02.xhtml ...
Parsing OPS/xhtml/33_chapter33.xhtml ...
Parsing OPS/xhtml/39_chapter39.xhtml ...
Parsing OPS/xhtml/back01.xhtml ...
Parsing OPS/xhtml/34_chapter34.xhtml ...
Parsing OPS/xhtml/40_chapter40.xhtml ...
Parsing OPS/xhtml/35_chapter35.xhtml ...
Parsing OPS/styles/stylesheet.css ...
Parsing OPS/xhtml/07_chapter07.xhtml ...
Parsing OPS/xhtml/cover.xhtml ...
Parsing OPS/xhtml/08_chapter08.xhtml ...
Parsing OPS/xhtml/09_chapter09.xhtml ...
Parsing OPS/xhtml/copyright.xhtml ...
Parsing OPS/xhtml/10_chapter10.xhtml ...
Parsing OPS/xhtml/11_chapter11.xhtml ...
Parsing OPS/xhtml/title.xhtml ...
Parsing OPS/xhtml/12_chapter12.xhtml ...
Parsing OPS/xhtml/fm.xhtml ...
Parsing OPS/xhtml/13_chapter13.xhtml ...
Parsing OPS/xhtml/42_chapter42.xhtml ...
Parsing OPS/xhtml/14_chapter14.xhtml ...
Parsing OPS/xhtml/01_chapter01.xhtml ...
Parsing OPS/xhtml/15_chapter15.xhtml ...
Parsing OPS/xhtml/16_chapter16.xhtml ...
Parsing OPS/xhtml/02_chapter02.xhtml ...
Parsing OPS/xhtml/17_chapter17.xhtml ...
Parsing OPS/xhtml/18_chapter18.xhtml ...
Parsing OPS/xhtml/03_chapter03.xhtml ...
Parsing OPS/xhtml/19_chapter19.xhtml ...
Parsing OPS/xhtml/20_chapter20.xhtml ...
Parsing OPS/xhtml/04_chapter04.xhtml ...
Parsing OPS/xhtml/21_chapter21.xhtml ...
Parsing OPS/xhtml/22_chapter22.xhtml ...
Parsing OPS/xhtml/05_chapter05.xhtml ...
Parsing OPS/xhtml/23_chapter23.xhtml ...
Parsing OPS/xhtml/24_chapter24.xhtml ...
Parsing OPS/xhtml/06_chapter06.xhtml ...
Parsing OPS/xhtml/41_chapter41.xhtml ...
Parsing OPS/xhtml/25_chapter25.xhtml ...
Parsing OPS/xhtml/26_chapter26.xhtml ...
Reading TOC from NCX...
Merging user specified metadata...
Detecting structure...
Removed first image
Removing OPS/xhtml/cover.xhtml as it has no content
Flattening CSS and remapping font sizes...
Source base font size is 12.00000pt
Removing fake margins...
Found 4481 items of level: p_1
Found 1 items of level: div_1
p_1 left margin stats: Counter({u'0': 4470, u'1em': 11})
p_1 right margin stats: Counter({u'0': 4477, u'4em': 3, u'1em': 1})
div_1 left margin stats: Counter()
div_1 right margin stats: Counter()
Cleaning up manifest...
Trimming unused files from manifest...
Creating AZW3 Output...
Serializing resources...
Python function terminated unexpectedly
u'cover.jpeg' (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 33, in gui_convert_override
File "site-packages\calibre\gui2\convert\gui_conversion.py", line 26, in gui_convert
File "site-packages\calibre\ebooks\conversion\plumber.py", line 1227, in run
File "site-packages\calibre\ebooks\conversion\plugins\mobi_ou tput.py", line 320, in convert
File "site-packages\calibre\ebooks\conversion\plugins\mobi_ou tput.py", line 21, in remove_html_cover
KeyError: u'cover.jpeg'