I had that message appear a few hundred miles after my recent oil change. What I did was to reboot the computer. I pressed down on the radio power switch for about 30 seconds until the screen went blank, and the computer reinitialized. (You can do this with the X3 running.) The message was gone after the reboot. If it returns I'll be making a service appointment. For now, the oil level appears to be at the top of the recommended range.
NB, eh? That was part of my 2500 mile maritime road trip this summer. The fact that there is one BMW dealer each in NB, NS, and NL did make me wonder how things would work out if I had a problem.