Thanks Dedas, am trying it now !

I just tried this solution, and for the first time in years I'm able to play the first map out! I'm running it under Vista Ultimate 64-Bit, FYI. Had to run it in 95 compatability mode with graphics set to low-res in the compatability tab, and it is running with the 1.2 patch.

Was there a website that you found that told you to use the lower case p? What is the address, for other Chaos Gate issues?

You folks are still playing this game? Awesome. I've still got it running on my old HP pavilion. I've discovered a way to create whole new campaigns for the game:
 
1.) Navigate to C:\Program Files\Random Games\Chaos Gate\Maps
This is where all the single player campaign maps are. Save them off somewhere else so you can restore the original campaign later on if you want to.
 
2.) start up the scenario editor that comes with the game. Under "FILE", click "Generate Random Map." This brings up the same screen for generating a single random battle. All the elements are there for designing a particular battle, and the computer will generate the terrain and the enemy forces. When the computer is done, it will leave you in the scenario editor so you can make any additional changes if you are handy with the editor. One quick and easy thing you can do is click MISSION SETUP under the SETUP button. There you can add a title and a mission briefing. You can also check off which units can take part in the mission. This allows you to have Captain K and the other high levels participate in your very first missions. Please note that if you add text to the mission briefing it will only show up in the mission briefing pop up in the battlefield. The Cathedral Bridge screen will still show the original campaign's briefings.
 
3.) When you are done with the generated mission, click FILE and then SAVE AS and give it the same file name as the map you wish to replace in C:\Program Files\Random Games\Chaos Gate\Maps. I.e. After you create your first mission, save it as Chapter01.MAP in C:\Program Files\Random Games\Chaos Gate\Maps. After you finish creating your second mission save it as Chapter02.MAP. Etc etc etc.
 
4.) when you start the single player campaign, you will start out at the first mission, get the Cathedral Bridge briefing for the original first mission, but the battlefield briefing pop up will show your new first mission. In the addition to the new set of missions you've created, you'll still get the randomly generated secondary missions too. The thing about having a new campaign is that Captain's K command will start out with their normal lack of experience and the new campaigns will allow them to progress just like the old campaign did. And there's the fun of seeing the marines get picked off one by one as the missions go by. I missed those two things when I got tired of playing the old campaign.
 
5.) Cautions. A.) Make sure you have no mistakes (like forgetting to specify an mission ending condition)in any of your missions because once you start the campaign, the computer saves the campaign maps off somewhere else as it goes through the campaign. If you've made a mistake in the Chapter05.MAP, you will have to restart your campaign all over again after you fix it. B.) In the Scenario Editor's Generate Random Map screen, the size and power of the Chaos forces are determined by the Level of Difficulty slider. Since the Ultramarines start at low experience in the beginning, you will have to do some play-testing to determine what the difficulty level should be for each mission. I.e., if you set the Difficulty level at 10 for the Chapter01.MAP mission, your guys will get wiped out even if you have Captain K, the Chaplain, and three Dreadnoughts with you. Match the difficulty level of the first mission to the experience level of Chapter01.MAP and then step it up in successive missions.
 
Have fun, folks!
 
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