Adobe Digital Edition 4.5.7 can not open my books any more (error!)

I have got a sincere problem with Adobe Digital Edition 4.5.7, since April 2018 (before it worked perfect!! ) When I try to open a book, it pops up: "there are errors found in the item" - but this comes up with every e-book I try to open in the 4.5.7. reader!. So I can not open my books any more  (which I bought, quite expensive). Does anyone have a solution? I am desperate. Need the books for a thesis. Thank you in advance!