Ok you can deauthorize Adobe Digital Editions with your current Adobe ID by pressing Control-Shift-D. You can also deauthorize your Nook by pressing Control-Shift-E while in Adobe Digital Editions.
Please keep in mind that all of your purchased content is current under your previous Adobe ID. With ADE 2.0 you will still be able to read this content in ADE, as it supports multiple Adobe IDs, but you would not be able to transfer the content to your Nook since it would then be on your new Adobe ID.
In order to resolve this you will want to contact the eBook provider and request that they reset the activations on your purchased content. You will then want to download and activate the content under your new Adobe ID in ADE for it to be tied to your new Adobe ID. Alterantely you can deauthorize and reauthorize your Nook with the old ID if you want to access the previously purchased content.