Mr Mike wrote:

When I access my address book, there are several blank contacts lists
listed. I have to open the dropdown list and select the botton
contact list to
select a person. I recall seeing this problem before but cannot seen
to find the solution on how to remove these blank entries.

Depends entirely on your Outlook version, which you decided to keep secret.

BTW, how does this happen?

There are multiple causes, with importing among them.
--
Brian Tillman