Since your 6.03 worked OK on a 2 meg book, it is possible it is the 18 meg book, however the messages under the download indicated it worked OK.
https://www.mobileread.com/forums/showthread.php?t=52321
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When I tried opeing the above book in Calibre 6.03 I got the following:
When I hit View, it opens the window, acts like it's opening the book, then I get:
Error: Could not open ebook
(267, 'The directory name is invalid')
Traceback (most recent call last): File "C:\Program Files\calibre\library.zip\calibre\gui2\viewer\main .py", line 56, in run
File "threading.pyo", line 477, in run
File "calibre\ebooks\oeb\iterator.pyo", line 140, in __enter__
File "calibre\customize\conversion.pyo", line 217, in __call__
File "calibre\ebooks\epub\input.pyo", line 106, in convert
File "calibre\utils\zipfile.pyo", line 1013, in extractall
File "calibre\utils\zipfile.pyo", line 1001, in extract
File "calibre\utils\zipfile.pyo", line 1037, in _extract_member
File "os.pyo", line 157, in makedirs
WindowsError: [Error 267] The directory name is invalid: 'c:\\users\\sharon\\appdata\\local\\temp\\calibre_ 0.6.3_umezmf_ebook_iter\\OEBPS\\images\\aux'
When I hit "next page"(? the purple right arrow) I get:
ERROR: ERROR: Unhandled exception
AttributeError: "EbookViewer' object has no attribute "current_index'
Traceback (most recent call last):
File "C:\Program Files\calibre\library.zip\calibre\gui2\viewer\main .py", line 247, in <lambda>
File "calibre\gui2\viewer\documentview.pyo", line 549, in next_page
File "C:\Program Files\calibre\library.zip\calibre\gui2\viewer\main .py", line 607, in next_document
AttributeError: 'EbookViewer' object has no attribute 'current_index'
Hopes this helps you, I'm not anxious about this, just a book I thought I'd peruse.
Thanks for all your hard work.
AJ