Thank you very much but the problem isn't with reader for PC, it recognizes the ereader, but Digital Editions not.
I assume this is all on the same machine?
You need to have Sony Reader installed before ADE will recognize most (all?) Sony eReaders, even if you never actually run Sony Reader.
(Why Sony make it so complicated I don't know.)
But from what you say it does sound as if you have Sony Reader installed.
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There are issues on ADE2.0 with some eReader devices.
Even if you get it to recognize a Sony device, ADE will probably fail to work with Overdrive library books when the device is plugged in.
ADE won't even read the books on the computer itself.
There are lots of bugs in ADE2.0 (and 2.0.1). 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