Just for clarity:

1) Are you sure you have Jazz2 version 1.23 and not 1.00G?
2) You are talking about the list server patch right (which is a .reg file)? And not the 1.23 patch.
3) And if you are sure it is the list server patch, you did double click and install it right? Sometimes I get people who just throw the file in their JJ2 directory and don't do anything with it.

If option 1 is the case. BUY the game somewhere. Don't download it from a certain abandonware site like you most likely did. That site contains an OEM version which isn't compatible with the final version.