Its a permission problem. To fix it you need to SSH into your phone and run the following commands in terminal:
ssh root@<your phones IP address>
*Type your password
cd /
cd Applications/
chmod +s Installer.app/Installer
chown -R root:wheel Installer.app
reboot
*****
That should fix your problem. This happens all the time to me and its quite annoying. Also make sure your queue is cleared before trying to install again.