This is not a Macromedia Lingo problem, it is access to a plug-in issue. In order for Director to access the plug-in it uses the Carbon Library to set up the ABI to both the plug-in and OS X properly. So, you need to add CarbonLib to the project. However, be aware that CodeWarrior hasn't supported Mac OS X platform development for several years. You may want to look for a plug-in code example for Director that uses Apple's XCode development tools.
Sorry I can't be of more help than that.
---Tom