Pbdirectory wont install

When I try to install phone book directory from module admin this is what I get.
Downloading pbdirectory
Untarring…Error(s) downloading pbdirectory:

* Could not remove old module /var/www/html/admin/modules/ to install new version

you must have a permission problem, the module install process untars the new module into the _cache, then removes the old one before moving the new one over. Check you permisssions.