Assuming that you're using the Codewarrior IDE, does the file name appear in the project window? If not, then IDE's build system doesn't recongize it. If the file's name is visible, check to see if it's part of the target build. That is, see if there's a black dot in the target column (it has a little red bullseye icon with a black arrow in it at the top of the project window). The black dot in this column indicates that the IDE will use the header file as part of the build process. No dot, and the IDE ignores it.
---Tom