ePub conversion problem

I have a couple of .ePub ebooks and can't get Calibre to convert them to .MOBI. Even the Calibre Reader can't open them and gives me the message:

Traceback (most recent call last):
File "site-packages\calibre\gui2\viewer\main.py", line 40, in run
File "threading.py", line 504, in run
File "site-packages\calibre\ebooks\oeb\iterator\book.py", line 99, in __enter__
File "site-packages\calibre\customize\conversion.py", line 239, in __call__
File "site-packages\calibre\ebooks\conversion\plugins\epub_in put.py", line 161, in convert
File "site-packages\calibre\utils\localunzip.py", line 217, in extractall
File "site-packages\calibre\utils\localunzip.py", line 204, in _extractall
ValueError: Not a ZIP file

When I try to convert it to MOBI, I get the error message:

calibre, version 0.9.9 (win32, isfrozen: True)
Conversion Error: Failed: Convert book 1 of 1 (Descent, The)

Convert book 1 of 1 (Descent, The)
Resolved conversion options
calibre version: 0.9.9
{'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': None,
'debug_pipeline': None,
'dehyphenate': True,
'delete_blank_paragraphs': True,
'disable_font_rescaling': False,
'dont_compress': False,
'duplicate_links_in_toc': False,
'embed_font_family': None,
'enable_heuristics': 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 0x037A62F0>,
'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_file_type': u'old',
'mobi_ignore_margins': False,
'mobi_keep_original_images': False,
'mobi_toc_at_start': False,
'no_chapters_in_toc': False,
'no_inline_navbars': True,
'no_inline_toc': False,
'output_profile': <calibre.customize.profiles.KindleOutput object at 0x037A6630>,
'page_breaks_before': u'/',
'personal_doc': u'[PDOC]',
'prefer_author_sort': False,
'prefer_metadata_cover': False,
'pretty_print': False,
'pubdate': None,
'publisher': None,
'rating': None,
'read_metadata_from_opf': u'C:\\Users\\BLUESU~1\\AppData\\Local\\Temp\\calib re_0.9.9_tmp_i1r308\\bqspmu.opf',
'remove_fake_margins': True,
'remove_first_image': False,
'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,
'unsmarten_punctuation': False,
'unwrap_lines': True,
'use_auto_toc': False,
'verbose': 2}
InputFormatPlugin: EPUB Input running
on C:\Users\BLUESU~1\AppData\Local\Temp\calibre_0.9.9 _tmp_i1r308\p2cynm.epub
EPUB appears to be invalid ZIP file, trying a more forgiving ZIP parser
Traceback (most recent call last):
File "site-packages\calibre\ebooks\conversion\plugins\epub_in put.py", line 154, in convert
File "site-packages\calibre\utils\zipfile.py", line 751, in __init__
File "site-packages\calibre\utils\zipfile.py", line 786, in _GetContents
File "site-packages\calibre\utils\zipfile.py", line 801, in _RealGetContents
BadZipfile: File is not a zip file

Python function terminated unexpectedly
Not a ZIP file (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 186, in main
File "site-packages\calibre\gui2\convert\gui_conversion.py", line 31, in gui_convert_override
File "site-packages\calibre\gui2\convert\gui_conversion.py", line 25, in gui_convert
File "site-packages\calibre\ebooks\conversion\plumber.py", line 1009, in run
File "site-packages\calibre\customize\conversion.py", line 239, in __call__
File "site-packages\calibre\ebooks\conversion\plugins\epub_in put.py", line 161, in convert
File "site-packages\calibre\utils\localunzip.py", line 217, in extractall
File "site-packages\calibre\utils\localunzip.py", line 204, in _extractall
ValueError: Not a ZIP file

When I try to read one of the .ePub books in Sigil, I just get a "cannot open" message. On FireFox's EPUBReader, I get a "format is corrupted." When I submit it to Kindle Convert, it says it can't translate and there might be a DRM problem (It should NOT have DRM).

I'm attaching one of the books for you to check out. I got them from a friend who swears he bought them and I paid him for them, so I had no reason to believe they are mis-formatted until I tried to read and convert them.