As per their site (http://ebookstore.sony.com/downpage/index_b.html):
"Reader Store is now closed in the US and Canada
As announced by Sony, Reader Store in the U.S. and Canada closed on March 20, 2014, and customers were transferred to Toronto-based eReading company, Kobo. Accordingly, Reader Store accounts are now closed and access to purchased content is no longer available.
To read more details, click here: https://us.en.kb.sony.com/app/answers/detail/a_id/45014 "