When you install a content pack it will check the system registry for the install location for iClone. It may be that the system registry has not been successfully updated with this information when you originally installed iClone.
You could try uninstalling iClone and doing a fresh install to try and eliminate this as a possibility. Also if you do reinstall iClone make a note of the location for your Default (not custom) content you are installing. This way you could manually check with Windows Explorer if the files are actually installed, even if they are not showing up in iClone.
If after this you still have problems then please contact Reallusion Support using the link below. They will be able to advise you further on this problem.
http://www.reallusion.com/CustomerSupport/User/QForm.aspx
Peter
Forum Administrator
www.reallusion.com