I am unable to download or return ebooks. I get a message saying: "Error getting license or Error returning item. Licesnse serve communication problem. E_AUTH_BAD_DEVICE_KEY_OR_PKCS12"

For this problem, you need to deauthorize and authorize ADE again

Launch ADE

Help -> Erase authorization.

ADE will be deauhorized.

Now again AUTHORIZE ADE

Help-> authorize computer.

Error will be fixed !!