. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reference— Camera 7-9
the next picture you take will be numbered 1, then 2, then 3, and so on,
even if those numbers are already in use.
Therefore it is possible that you may have several images on a PCMCIA
card with the same number. Duplicate image numbers do not cause any
functional problems; however, you can avoid potential confusion by
occasionally erasing or formatting the PCMCIA card after copying all
needed images to your computer hard disk.

ISO Warning

“ISO” blinks as a warning on the LCD if you try to take a picture and the
Nikon N90s is not set to a supported ISO as listed in the Specifications
appendix.
If you take a picture and the camera is not set at a supported ISO, you will
be able to take one picture (with unpredictable results), but then the
camera back will automatically reset to a supported ISO. “ISO” blinks on
the camera back LCD until you take another picture or until the camera
goes to sleep; the new ISO will be displayed on the camera top LCD if the
N90s ISO button is pressed.
ISO
Blinking