SAMPLE ERROR MESSAGES with catkin_make   

If there is an error message that says that something is 'missing' or 'can't find', you will probably need to set an environment variable.
EXAMPLE:
/usr/local/lib/libdynamixel_driver.so.52: error adding symbols: DSO missing from command line
collect2: error: ld returned 1 exit status
         # Set environment variables (show complete path for libdynamixel_driver.so) [See example below, the area in green is where your path will go]
         $ export ROS_PACKAGE_PATH=~/home/connor/catkin_ws/install/lib:$ROS_PACKAGE_PATH
         # If more than one path is needed separate them with a " : "

But, I have encountered an error message in the connor workspace  /usr/bin/ld: cannot find -ldxl.
      # This error is looking for the .a file. You should be able to set an environment variable. Unfortunately, although I tried setting the path and tried
      # copying the file to a different location, the file still can't be found.
      # Answer to problem: the SDK wasn't installed.

To clean up old references to packages removed when starting over
         rm -rf build devel

If Invoking "make" failed and you just can't figure out why.......
         You may need to source your setup files again