[ascalise]

Whenever I try to save a book to disk using "Save single format" I get the following error message:

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calibre, version 0.8.10
WARNING: Could not save some books: Could not save some books, Click the show details button to see which ones.

War and Peace
Requested formats not available
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I have tried a number of different formats: RTF, TXT, PDF. The same error occurs with all books and formats.

Any hints will be much appreciated