I bought a book but it won't let me put it on my e-Reader

I bought a book from an online book store which said I had to download it through Adobe Digital Editions.  Great!  I did that.  Paid money for my book.  But then I tried to transfer it from the ADE to my eReader and it says I have no permission to copy the book!!!  I PAID for the book!!!!  I want to READ the book!!!!  How do I override this so that I can actually get my money's worth out of the book???