[Nedfro]

Hello
When I try to add books to calibre I get following error message (German):
calibre, version 2.74.0
FEHLER: Fehler während des Hinzufügens: Es konnten keine Bücher hinzugefügt werden. "Details anzeigen" anklicken für weitere Informationen

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Hinzufügen des Buches fehlgeschlagen:Andrzej Sapkowski The Last Wish
/home/remo/E-Books/The Witcher Books - Andrzej Sapkowski/The Witcher Books - ePub/01-Short Stories-The_Last_Wish (1993).epub
Mit Fehler:
Traceback (most recent call last):
File "site-packages/calibre/gui2/add.py", line 379, in add_book
File "site-packages/calibre/db/legacy.py", line 217, in create_book_entry
File "site-packages/calibre/db/cache.py", line 61, in call_func_with_lock
File "site-packages/calibre/db/cache.py", line 1529, in create_book_entry
File "site-packages/calibre/db/backend.py", line 822, in execute
File "src/cursor.c", line 231, in resetcursor
ReadOnlyError: ReadOnlyError: attempt to write a readonly database

The books I tried to add are on an NTFS formatted HDD and in 3 different formats (EPub, azw3, PDF), neither of them work. I have also tried copying the files to my /home partition (I'm running Linux Mint 18 on an SSD), wich didn't help.
In the FAQ it says: "Linux kernels mount devices read-only when their filesystems have errors.", but since I have also copied the files onto my main drive (wich im pretty sure isn't read-only), i don't think that this will help (Plus I don't want to f*ck around with my HDD since i'm pretty new to this stuff).

Hope someone can help
Thanks and greets
Ned