Have you read the help page at Error: E_ADEPT_REQUEST_EXPIRED | Digital Editions
Otherwise, other thing that could be wrong is the ACSM has expired and you might need to get a new one from the place you purchased the ebook from.
This doesn't help at all. There is nothing wrong with my date and time, and the ascm file should open in my ADE and start fulfilling the file to become the ePub that I can transfer to the Nook. After uninstalling and reinstalling (several times), moving all my old files to my external hard disk, checking all the security accesses on the program, running ADE as an Admin, and getting messages like "Error opening file welcome.epub" and E_IO_CANNOT_OPEN I can finally open the old files, but when I download a new one, It just doesn't appear anywhere. When I go to add to the library from the ascm file, I get the above error message.
Looks like if this