I think I was using the NewSoftSerial library. I downloaded it, and pasted it into the /library/ folder at my arduino location. Is that all I had to do?
I have also since tried it without the stream versions, and still the same error.
I have been told that I may have to check the instantiation? I'm not sure what this is, as I only saw it online in relation to the ump3 device.
When attaching my uno to the rmp3, am I correct in just lining up all the pins and attaching? The activity light flashes for a brief moment on the rmp3, then just goes off, and Windows makes the "hardware plugged in" sound, then the removed sound, while the uno is just loop playing the blink programme that I loaded onto it.