I did some more research and find that this issue is yet another huge restriction that TB puts on their address books and strange no one would help with this. I was told of the restriction where collected addresses could no be dragged to any mailing list (which makes no sense why they'd add this restriction).

But there is a new restriction I found that no one mentioned. That is a mailing list has to be contained inside one of the existing address books and that it can accept contacts ONLY from that same address book! Since TB can use multiple address books it makes no sense why a mailing list can contain entries from only the one address book it is within.

It is too bad TB puts these restrictions on it's mailing lists, but worse that it is not publicized well. In this case, there are no "corrupt" address books. A contact should be able to be dragged to a mailing list from any address book, including the "All Address Books" or "Collected Addresses". Certainly not limited to only one address book.

I too found the same problem and was unable to add an existing address to a mailing list using drag and drop. However, by clicking on the ellipsis next to the list and selecting Properties it was possible to add the address to the list Joe