Setuid command seems to not working

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http://ubuntuforums.org – I had windows application installed on Linux computer, for example, in Demo directory. And in Demo folder, I have files directories structure as follow -rwxrwxrwx spuser spuser aaa.dll -rwxrwxrwx spuser spuser bbb.ttf -rwxrwxrwx spuser spuser ccc.ref -rwsrwxrwx spuser spuser DemoApp.EXE <= I've set setuid command on this file drwxrwxrwx spuser spuser icons drwxrwxrwx spuser spuser secure drwxrwxr-- spuser spuser lang If I run DemoApp.EXE with spuser privilege, it work fine, DemoApp.EXE can read files within lang directory. But when I run DemoApp.EXE with ordinary user privil (Hardware)