just uploaded a test code pkg to our RAM community When I tried to download it, It prompts to save the file as "tgz" type when the actual file is .tar.z

This happens on InternetExplorer when the mimetype is not registered for that extension in the server AND the file being downloaded is a tar.Z file (tar.z). Internet Explorer gets confused because it didn't get a mime type for it, but it sees it is a tgz format, so it treats as a tgz format and brings up the bad name request, ignoring the name in the download request itself.

Your websphere admin will need to map .Z to mimetype application/x-gzip . Hopefully that will fix the problem.