If you've clicked on an "Online access" link to an ebook on iDiscover to find that you're only given a message saying "The connection has timed out", you've probably found a link to an electronic legal deposit book. Many publishers are now fulfilling their legal deposit obligations by depositing electronic rather than print books with the six legal deposit libraries, including the UL.
You can spot an ELD ebook by the wording of the link from iDiscover: "Online access restricted to designated PCs in the main UL and affiliate libraries".
Note: If the ebook is not electronic legal deposit content, please contact the ebooks@cambridge team on ebooks@lib.cam.ac.uk who will investigate the issue for you. Please send title information and a screenshot of the error message if possible.