Paul, I assume you have the camera set to 400 iso? All I can think of is this camera is old. It could be an issue with the meter, the contacts on the controls, battery contacts. They could have corrosion. Also if there were any clouds in the sky, the sunny16 rule says to go to 11 for that.
I never checked any of my cameras, I should try it and see if it works. ISO values in digital cameras are all non-standard, so if we were talking about a digital camera I'd think that would play a part.
Did you go ahead and take a shot and look at it? If so, did it look underexposed?
I have a SLR like it, the KR-10 Ricoh, I would look at the battery if mine were doing this, but you said yours is new. Hmmm. No idea.
Maybe test your battery with a voltmeter if you can, might be a bad new one?
[edit]
Well, now that I read the post above, I think we have the answer.
I never knew latitude was a factor. Makes sense!