Hi Ken,
If the problem is affecting all content then it may be you have the divider between the folders and the content too far to the right so you can't see the content thumbnails. To resolve the problem just drag the divider (the dotted line) over to the left. This will then display the content thumbnails.
Please see section 7of the page below for how to do this.
http://manual.reallusion.com/iClone_6/ENU/Pro_6.0/04_Introducing_the_User_Interface/Content_manager.htm
If the problem is only affecting some content, then it may be that this is old content that was supplied with the .VNS extension.
To resolve theproblem you can simply re-name the file extension from VNS to the correct extension instead. Then they will be recognised by iClone 6 and can be used in the normal way.
So for example, find the empty folder in Content Manager and then right click it and choose "Find File". This will open File Explorer where you can change the file extension from .VNS to .iProp for props, .iMotion for motion files, .iAcc for accessories and so on. They will then show up in iClone 6.
The only exception to the above is for avatars. These can't simply have the extension changed to.iAvatar. To use these files you will need to resave them first in iClone 5. This will then give them the correct .iAvatar extension which will then be recognisedby iClone 6.
Note: Many older VNS packs have been updated to the new formats. Please do try downloading any avatar packs again first just to check.