Calibre will not save to disk

[mrbillb]

I had not been having any problems with this, but now I am.
the detailed information follows:


Save books (0 of 1)
Traceback (most recent call last):
File "/usr/bin/calibre-parallel", line 19, in <module>
sys.exit(main())
File "/usr/lib/calibre/calibre/utils/ipc/worker.py", line 99, in main
result = func(*args, **kwargs)
File "/usr/lib/calibre/calibre/ebooks/metadata/worker.py", line 245, in save_book
save_to_disk(db, task, path, opts, callback)
File "/usr/lib/calibre/calibre/library/save_to_disk.py", line 258, in save_to_disk
failed, id, title = True, x, db.title(x, index_is_id=True)
File "/usr/lib/calibre/calibre/library/database2.py", line 489, in get_property
row = self.data._data[idx] if index_is_id else self.data[idx]
IndexError: list index out of range
Error in sys.excepthook:
Traceback (most recent call last):
File "/usr/lib/python2.6/dist-packages/apport_python_hook.py", line 90, in apport_excepthook
if pr.check_ignored():
File "/usr/lib/python2.6/dist-packages/apport/report.py", line 752, in check_ignored
dom = self._get_ignore_dom()
File "/usr/lib/python2.6/dist-packages/apport/report.py", line 713, in _get_ignore_dom
dom = xml.dom.getDOMImplementation().createDocument(None , 'apport', None)
File "/usr/lib/python2.6/dist-packages/cssutils/__init__.py", line 139, in createDocument
raise NotImplementedError
NotImplementedError

Original exception was:
Traceback (most recent call last):
File "/usr/bin/calibre-parallel", line 19, in <module>
sys.exit(main())
File "/usr/lib/calibre/calibre/utils/ipc/worker.py", line 99, in main
result = func(*args, **kwargs)
File "/usr/lib/calibre/calibre/ebooks/metadata/worker.py", line 245, in save_book
save_to_disk(db, task, path, opts, callback)
File "/usr/lib/calibre/calibre/library/save_to_disk.py", line 258, in save_to_disk
failed, id, title = True, x, db.title(x, index_is_id=True)
File "/usr/lib/calibre/calibre/library/database2.py", line 489, in get_property
row = self.data._data[idx] if index_is_id else self.data[idx]
IndexError: list index out of range

None of the messages mean anything to me, so I need some help.

Except for errors I have noted in other posts, the conversion process works OK. I get this error only when I want to save to disk.