One possible reason is that it takes too long time between downloading .acsm file and fulfilling book, which makes the fulfillment ticket expired. The expiration time depends on the cph.org. It could be from couple of minutes to even couple of hours. You may check with cph.org.
The other possible reason is that your computer time is not correct. Please be sure that your computer is set to correct date, *time*, and time zone. I recommend you to set your computer time auto sync with Internet time server.
I'm having the same problem as Phil and am also frustrated. I have a new computer with Windows 8, have checked the time and time zone and both are correct. I have downloaded books from my local library, but have not been able to drag them into DE. I get the same error message. Can somebody please help with this? I've found no way to communicate directly with Adobe.
My old computer ran on Windows 7 and I never had any problems with it.
Sorry, but this message is unique to a discrepancy between your computer
and the source. The DATE, time and time zone must be accurate to where you
are. I'm not sure how Win 8 handles these settings, so I can't help you
discover whether there's some gremlin or possibly two places to look for
the process of setting these values.