If Сontra launcher does not work, you have to copy Contra files manually. To do so, copy following files and folders from Contra mod into your Generals Zero Hour folder:
And delete Scripts folder from Data folder (ZH\Data\Scripts) - if you don't Delete Scripts Folder, AI will not work!
Some of these files are already existing in your Generals Zero Hour. It is recomended to backup original files before overwriting them.