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Originally Posted by gbm

Here is your problem:

From calibre FAQ:

If Google Drive was the culprit I would expect all versions of Calibre not to be able to open the books. Only the latest version has problems opening some of the book. Version 6.0 works without any issue.
In fact I tried to open another book outside Google Drive folder and had the same problem. Renaming the book fixed the problem.
The last update is broken.