I had the same problem myself with version 2.0: ADE would not allow me to authorize my computer. I received the error message: E_AUTH_NOT_READY. The fact is, my computer is already authorized. Version 2.0 did recognize my Sony eReader however.
Following advice in a different thread, I uninstalled Version 2.0 and installed Version 1.7.2. It recognized my eReader successfully. It also automatically recognized that my computer was already authorized and told me that I did not need to authorize.
I'm going to stick with Version 1.7.2 until a new version is released. The problem seems to lie with version 2.0 authorization.
I hope the next version upgrades without requiring an uninstall because when I uninstalled 2.0 before reinstalling, I lost my library.