Copy function

Hi - I'm having trouble copying text from an eBook. When I first opened Digital Editions I could highlight and copy parts of the text, but then it stopped on about the 5th page. Now the "copy" button is greyed out and the Ctrl C function doesn't work either. I tried rebooting my computer but it didn't help. I'm using the copy function to take some study notes as this is one of my prescribed texts. Any thoughts?