For most Sony readers you need a special driver for it to appear in ADE (typical irritating Sony).
To install the Sony driver you must install Sony Reader (free); even if you don't use Sony Reader the driver will get installed.
If you are going to use Overdrive library books with the Sony you will probably hit one of the (many) bugs in ADE2.0.
1.7.2 is the best solution to that problem.
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.
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
Thank you for your answere!
I first installed ADE 1.7.2. successfuly. Deauthorized and authorized my computer - just for being sure. I connected my prs-t1 but still it did not appear in the library.
Then I updated the firmware provided on http://www.sony.at/support/de/product/PRS-T1 or http://esupport.sony.com/US/p/model-home.pl?mdl=PRST1&template_id=1®ion_id=1&tab=downlo ad#/downloadTab . This firmware update included a programm called Reader for PC (which replaced Reader Library). This programm is connected to my ADE-library and that way I am able to transfer my books to the reader. The driver was not the problem - the firmware was the key to the riddle.
Mission accomplished - thank you so very much!!!