We will need more information, to figure out what's wrong. How do you export? using "File > Export > Versions, masters", "File > Share", or using the Media Browser?
Are your images raw or jpegs? Are the master image files managed or referenced? And where is your Aperture Library located?
Do you see the Nikon images in Aperture in the Browser, or do you only see your sony pics in Aperture?