It's very possible the light was activate by accident bluewhite4. As dwayneg mentioned, you can see what lit the msg light by pressing the msg key while the endpoint is idle. You will then see the name/ext of whatever lit the light in the endpoints LCD. You can then press # to return the call, or press * to turn the light off. This is very common on this platform with new users. They call an extension and then press the msg key thinking that they are going to leave a message, but all they do is activate the called extension's message light.