I have exactly the same issue - http://www.dexterindustries.com/topic/serial-error-with-birckpi/
I have got the LED test to work, however when I try any of the example code for using sensors or motors they all fail. Sometimes with an error message (as in that link) but normally with no response. (other than the ‘print’ command working in python telling me something is meant to happen).
It looks like there may be ‘feature’ of raspbian that sends log-in prompt information on the serial pins; but that interferes with the connection between BrickPi and Pi [as that tries to use the pins). There is a fix to turn this off manually in the older version of the SD card-image (i.e. older version of Raspbian) and that seems to have worked for someone else.
However I can’t get it to work on the current edition. I’m going to try tonight (or tomorrow) to use an older image and see if results improve. If you can do the same you may want to try that.
I have one of the first ‘modelB’ Pis - I imagine there may be some small differences to how Pi2 and Pi3 (models A or B) work that mean the problem isn’t experienced by everyone.