Hi folks,<br><br>I'm wondering why bjam reports the following error:<br><br>/cygdrive/c/mse/proj/boost-build/build/project.jam:602: in object(project-attributes)@123.set from module object(project-attributes)@123<br>error: usage-requirements &lt;include&gt;.. &lt;hptns-stl-version&gt;3 have non-free properties &lt;hptns-stl-version&gt;3<br><br>for:<br><br>project moblib2<br>&nbsp; : usage-requirements &lt;include&gt;..<br>&nbsp;&nbsp;&nbsp; &lt;hptns-stl-version&gt;3<br>&nbsp; ;<br><br>Why do properties listed for usage-requirements have to be 'free'?<br><br>Merci beaucoup,<br>Mark<br>