Probably you've a very old version.
So you have to uninstall the game using and reinstall with new remaster setup file.
Please do the following:
1. Please download the game's installer file v7.1.4 from the download section of the game's product's page:
https://www.matrixgames.com/game/order- ... rld-war-ii
2. Once you have finished downloading the file, please fully unzip the downloaded file "OoBWWII-MultiSetupRelease-v7.1.4.zip" to a folder in your Hard Disk.
After unzipping, you should have two extracted files:
"OoBWWII-MultiSetupRelease-v7.1.4.exe"
"OoBWWII-MultiSetupRelease-v7.1.4.2"
3. Run "OoBWWII-MultiSetupRelease-v7.1.4.exe".
4. When asked to insert the serial number, please click on the "Next" button and don't use any serial number. Click on "Next" until the base game is installed.
5. Now you need to update the base game.
6. Please download the game's last update file v9.0.0 from the download section of the game's product's page:
https://www.matrixgames.com/game/order- ... rld-war-ii
7. Once you have finished downloading the file, please fully unzip the downloaded file to a folder in your Hard Disk.
8. Run the extracted file "OoBWWII-MultiUpdateComp-v9.0.0.exe".
9. When asked to insert the serial number, please click in the drop down menu "Select a New Product to Install... " and select "Order of Battle: Allies Defiant".
Type your "Order of Battle: Allies Defiant" serial number.
10. Click in the button "Check Serial".
You should see then the DLC name"Order of Battle: Allies Defiant" being added to the list of games displayed in the box named "Setup as detected a valid serial number for:".
11. Repeat steps 10 and 11 for your other expansions.
12. Then click on the "Next” button in order to proceed with the installation of the game.