This problem is actually quite common and often goes hand in hand with the "Medal Crash" problem. It happened to me as well and I followed these steps to solve it. I'll re-post the solution here as opposed to directing you to the sticky in this forum as this specific thread is one of the first results to pop up when I did a Google search for "Battlefield 2142 + Northern strike + unable to unlock". I probably went overkill with the restarts, but I was just paranoid - and hey, it fixed the problem for me and that's all that matters

1.) Completely uninstall the game manually. You need to delete the registry entries as well. If you need reference, apply the steps in this sticky: (http ://ww w.tacticalgamer.com/battlefield-2142-technical-support-faqs/118563-unmodified-content-error-solution-guide.html)

2.) Restart your computer.

3.) Reinstall Battlefield 2142 vanilla.

4.) Restart your computer.

5.) Apply patch 1.4.

6.) Restart your computer.

7.) Reinstall Northern Strike.

8.) Restart your computer.

9.) Apply patch 1.4 again.

10.) Restart your computer.

11.) Apply INCREMENTAL Patch 1.4 - 1.5.

12.) Restart your computer.

13.) Uninstall Punkbuster. Download this (htt p://w ww.evenbalance.com/index.php?page=pbsvcfaq.php), run the .exe, and click "Uninstall".

14.) Restart your computer.

15.) Install Punkbuster. Use the same file as above, but click "Install" instead of "Uninstall".

16.) Restart your computer.

17.) Update Punkbuster for Battlefield 2142. Download this (htt p://w ww.evenbalance.com/index.php?page=pbsetup.php), run the .exe, click "Add Game - Battlefield 2142", then click "Check for Updates".

18.) Restart your computer.

19.) Done.


Hope this helps.

-RT