This can be a genuine message. (It seems most messages from ADE are incorrect or incomprehensible, but it does occasionally get one right.)
Especially common on a loaned book when the loan expires.
Also, some vendors put time limits on sales, in which case you probably need to contact the vendor.
If you are trying to open a .acsm file, you can edit the file with a regular text editor to see expiry information.
Another possibility is that the time, timezone or daylight savings settings on your computer are incorrect,
or don't match what the server things they ought to be.