Removing Lists from Thunderbird

[Jim]

I have Thunderbird making addional list in Address book, it is 
duplicating the same email addresses.

I have a new list called Collected Addresses and if I clear out 
duplicate addresses
it won't allow me to Delete this List.

The email addresses I want to keep are in my Personal Address Book, How 
do I get rid of this new List, "Collected Addresses" I don't want it, 
it's just creating duplicates ?