The Sony Reader software does not need to be open for ADE1.7.2 to work with the Sony.
The Sony driver installed with the reader needs to be running; which it probably will be if the Sony Reader software is installed.
ADE should work even without the driver, but won't see the Sony.
It sounds as if somehow ADE1.7.2 has got it into its head that you are already in process of trying to access a book;
possibly this is a leftover from a far-distant install you had forgotten about?
Try saying NO to the 'Do you want to resume pending tasks?' message and seeing if that helps.