No able to use rosserial_arduino

edit

Hello guys, I built ROS indigo on my pi 2 and tried to use the rosserial_arduino (after making my workspace having rosserial metapackage with catkin_make install). The problem is that whenever i try to initialize serial communication with an arduino with rosrun rosserial_python serial_node.py /dev/ttyACM0,it just says : No such file or directory. I checked my ports with ls /dev and my arduino is on ttyACM0. Please help me out.

EDIT

This problem was solved by rebuilding my workspace with catkin_make install but new errors have crept up again :

This is the error now on executing rosrun rosserial_python serial_node.py /dev/ttyACM0

Traceback (most recent call last):
File "/home/pi/ros_catkin_ws/src/rosserial/rosserial_python/nodes/serial_node.py", line 39, in <module>
from rosserial_python import SerialClient, RosSerialServer
File "/home/pi/ros_catkin_ws/devel/lib/python2.7/dist-packages/rosserial_python/__init__.py", line 35, in <module>
exec(__fh.read())
File "<string>", line 1, in <module>
File "/home/pi/ros_catkin_ws/src/rosserial/rosserial_python/src/rosserial_python/SerialClient.py", line 51, in <module>
import diagnostic_msgs.msg
ImportError: No module named diagnostic_msgs.msg