@Boken-Lin , Kernel upgrade didn't go up to 3.13.0-68-generic for some reason.
I can only bring it up to 3.13.0-55-generic. insmod seemed to work, but the connection still isn't working.
After all those failed attempts, I decided to upgrade to the latest long-term supported kernel 4.1.13. I used the instructions shown at:
Then followed the instruction for installing the cp210x driver.
And the serial connection works now!