Error on simple script to open new tab

I am trying to run a simple script which simply opens a new tab, but am getting

execution error: An error of type -10810 has occurred. (-10810)

I am running on Yosemite.

This is the script:

#!/usr/bin/osascript

tell application "Terminal"
    activate
    tell application "System Events" to keystroke "t" using command down
    delay 2 
end tell