hi waynef, i get the error ? message in the iso panel with camera in auto or manual the way it looks is r5 or r7 and also r17 i have cleaned lens and camera contacts also changed memory card and formatted it in camera.fully charged battery.It does not seem to effect the photo image as this is as is. I will get in touch with Nikon tomorrow as the camera is only 5months old !!
The r7 or r17 is NOT an error. It is simply the normal display of memory buffer capacity (how many images it can hold before written to memory card, which depends of file size selected). See D90 manual page 65. NOT AN ERROR.
The blinking ? is an error symbol on some camera models, but the D90 Error list (page 255-256) does not mention it.
I do not recognize "ISO screen". I assume you mean the top LCD (near shutter button), called Control Panel in manual. I may be missing it, but the diagram on page 7 does not appear to show any possible ? symbol? On that page page 7 diagram, which number points to what you see?