why does this happen ?

[Moglex]

Thanks for the replies.
Joves, the main subject was the moon. I guess I overexposed it. I was in kind of a hurry. I thought the meter was centered, and maybe it was, but with that light source I guess it may have tricked the meter a bit.
Live and learn.

Unless you were using spot metering and the image of the moon was big enough centring the meter will guarantee to overexpose the moon if the sky is clear.

The thing to remember about the moon is that the exposure should be roughly the same as for any other brightly lit landscape!