I recently did a clean install of my Mac and re-installed Poser Pro 2010. I have noticed that when I go to add certain elements like hair or clothing I have been getting the message:

This material collection contains materials that do not exist. Would you like these materials to be created? 

When I click Yes nothing happens am I missing something? 

When you drag-drop a material collection be carefull where to release the mouse button.

When you release on the wrong object, you get this messsage.

If you select and then load, bu sure to have the right object selected before loding the material collection for that object. Or you get the same message.

Material collections are there to "only load" the materials. They do not load the hair or the clothing.

First you need to load the hair, then the material collection for that hair.

Those are 2 possibilities where you can get this message.

Something is happening.  You are adding materials to your selected object that it didn't have before.  They won't render because they have no mesh associated with them.  They're just clutter.

As vilters said, it means that you're loading a material for something other than what you have selected. 

The material collextion (mc6) is going to load a grouup of named materials. If the current object does not contain those names poser gives you the message. If you say YES Poser will create the extra materials even though they are not allocated to any surface and will not be displayed.