Difficulty installing wordpress plugin

Hi;

Whenever I add and install a wordpress plugin on my http://www.happyholidays.com site I get the message below yet the plugin never fully installs.
Downloading install package from http://downloads.wordpress.org/plugin/gravatargrid.0.9.zip.
Unpacking the package.

This does not happen on my other site http://www.kingtockers.com where the plugin automatically installs every time.

Any ideas as to why ??