Unity 4 can communicate with serial port?

I’m working on a script in c# for communicating with a micro-controller (8051) connected to the serial port and using

using System.IO.Ports;

and refreshing assets (Assets>Reimport All) isn’t making Unity find this library.
I keep getting errors like:

I’m getting out of ideas…

Thank you Graham Dunnett, I’ll try that.

[EDIT]
Changed the script name and class name, now its working.

Can’t believe I did such a stupid mistake, it cost me 2 weeks.