[murphy112]

I use calibre since a long time and it works fine for me. My books are on my NAS, no problems.
But since Calibre 2.49 I cannot import ebooks, updating to 2.50 changed nothing, downgrading to 2.47 changed nothing too. I always get a message like this
----------------------------------------------------------------------
Failed to add the book: Alfresco 5.0 - Quickstart: Dokumentenmanagement und Teamwork mit der freien Community Edition (German Edition)
C:\Users\achim\AppData\Local\Temp\calibre_fkxlfk\a mbxpk_add_books\0\Alfresco 5.0 - Quickstart_ Dokumentenmanagement und Teamwork mit der freien Community Edition (German Edition).azw3
With error:
Traceback (most recent call last):
File "site-packages\calibre\gui2\add.py", line 369, in add_book
File "site-packages\calibre\db\legacy.py", line 214, in create_book_entry
File "site-packages\calibre\db\cache.py", line 57, in call_func_with_lock
File "site-packages\calibre\db\cache.py", line 1519, in create_book_entry
File "site-packages\calibre\db\cache.py", line 1245, in set_metadata
File "site-packages\calibre\db\cache.py", line 1232, in set_field
File "site-packages\calibre\db\cache.py", line 1054, in set_field
File "site-packages\calibre\db\write.py", line 513, in set_books
File "site-packages\calibre\db\write.py", line 437, in many_many
File "site-packages\calibre\db\backend.py", line 820, in executemany
File "c:\cygwin64\home\kovid\sw\build\apsw-3.8.2-r1\src\cursor.c", line 231, in resetcursor
ConstraintError: ConstraintError: Foreign key violation: authors is still referenced

When starting Calibre in debug mode, I get the following message:

calibre Debug log
calibre 2.47 [64bit] isfrozen: True is64bit: True
Windows-7-6.1.7601-SP1 Windows ('64bit', 'WindowsPE')
('Windows', '7', '6.1.7601')
Python 2.7.9
Windows: ('7', '6.1.7601', 'SP1', 'Multiprocessor Free')
DeDRM v6.1.0: In __init__
DeDRM v6.1.0: In load_resources
DeDRM v6.1.0: verdir C:\Users\achim\AppData\Roaming\calibre\plugins\DeD RM\6.1.0
DeDRM v6.1.0: In initialize
Successfully initialized third party plugins: DeDRM && K4PC, K4Mac, Kindle Mobi and Topaz DeDRM && Inept Epub DeDRM && Ignoble Epub DeDRM && eReader PDB 2 PML && Inept PDF DeDRM
Starting up...
Started up in 10.73 seconds with 413 books

I don't know what is wrong. Can anybody help me to solve the problem?

Thanks in advance
murphy