There are problems with Sony readers and ADE2.0 working with Overdrive library books.
Maybe the same issue applies to Sainsbury books.
The only solution I found was to use the older but more reliable ADE v1.7.2.
No promises, but worth a try. Good luck.
There are lots of bugs in ADE2.0. Try replacing ADE2.0 with the older but more reliable v1.7.2.
(You can have them both installed at once if you like.)
Version 1.7.2, it is a little difficult to find, available on Adobe site for Windows and for Mac.
http://helpx.adobe.com/digital-editions/kb/cant-install-digital-editio ns.html
The forum software is sometimes corrupting the link above. There shouldn't be a blank in 'editio ns.html'. The following redirects to the same page: http://tinyurl.com/diged172