I have had this problem myself.  This is how I fixed it.

Old site:

Use backup & migrate to do a back up.
or
Use MySQL Admin and do a db dump

use text editor's search and replace to change name of the the old db to the name of the new db. (if name is different) (I have only had 3 places where this change was made.)

New site:

delete the settings.php file. (or rename if you want to keep a back up)
make a copy of the default.settings.php file and rename it to settings.php

run your site like you are installing drupal for the first time.
when done, use backup & migrate to import the db back up you make from the old site.

Done.

Hope this will help you like it did me.
--
Cory Gilliam
Knoxville, TN 37921
imaaxa@gmail.com
865.335.3250