Just upgraded to 0.6.18.
Same error during installation as already mentioned:
Traceback (most recent call last):
File "/home/kovid/build/calibre/src/calibre/linux.py", line 176, in setup_completion
ImportError: cannot import name titles
But calibre still crashes whenever I try to upload a book:
$ calibre
link hasn't been detected!
link hasn't been detected!
/usr/bin/calibre: line 11: 10481 Segmentation fault $loader "$@"
Part of the uploaded file is actually on the reader, it seems to crash halfway through the uploading process.
Again, never had problems uploading with any version prior to 0.6.17.