I have trouble reading my book "Head First Android Development" in O'Reilly Library - I either get 'We're sorry, but something broke in our book reader; an error of type undefined has occurred: undefined', or a request to login (I am logged in) or register on Safari.
Sometimes retrying helps, sometimes I have to go through table of contents to go further in book...
I don't know why there is 'preview' label; I own that book... I didn't have that much trouble with "21st Century C, 2nd Edition".
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