Problems with LIT format

I have a number of books on LIT format. Several of these books are on LIT format . Although the path shows click to open there is always an error SPINE IS EMPTYj as per the code below. Books with the formats of LIT and EPUB open without problem. What should I do?

calibre, version 0.9.14
ERROR: Could not open ebook: Spine is empty

Traceback (most recent call last):
File "site-packages/calibre/gui2/viewer/main.py", line 40, in run
File "lib/python2.7/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/lit_input.py", line 23, in convert
File "site-packages/calibre/ebooks/conversion/plumber.py", line 1183, in create_oebbook
File "site-packages/calibre/ebooks/oeb/reader.py", line 70, in __call__
File "site-packages/calibre/ebooks/oeb/reader.py", line 676, in _all_from_opf
File "site-packages/calibre/ebooks/oeb/reader.py", line 329, in _spine_from_opf
OEBError: Spine is empty