Media Library: Large size image option disabled

On the Settings->Media screen, what is the large size set to? If that size is bigger than the actual image you upload, then the large version won’t get created and that button will be disabled for that image.

The large size is set to 640 (height and width). As you can see from the link above, the image is larger than that.

Same problem!

Any one with a suggestion?

Is the radio button greyed out or is the text/button invisble at all?
For me:
I never use a medium format, so I did not specify one in the media settings. Then that button is always greyed out and no image size medium is created (saves space!!).
Next, if the choosen image to upload is smaller than size large, that button is also greyed out (you can easily see the size because full size is shown to the right of the large button).