Err message The camera is showing an ERR in the aperture area of the LCD area...I am not able to use the shutter button auto focus...Can someone suggest what to do?

Check the batteries

failure of the aperture unit is the usual cause - usually the contacts for the phase switch have come loose from the gear. You can find info on this by searching for the problem on the internet, including how to repair it.

This is an indication that the camera is not "talking" to the lens correctly. When you press the shutter button, the camera tries to focus, set light levels, and then shoot the picture. If it can't focus or set F-stop and shutter speed, then it can't shoot the picture and gives you the error indication. SO
1. You need to make sure the lens is an automatic lens capable of working with the D90. 2. You can take the lens off and back onto the camera a few times in case its a dirty contact issue or just didn't seat correctly. 3. Set the D90 to manual and make sure you move the AF selector on the front to M. Then you would manually adjust all the settings. That should take the auto-coupling out of the picture (pun intended)
4. If it still shows error when in total manual mode, there may be something wrong in the camera itself. Before giving up, do a total system reset on the D90 (I assume you have the manual).

Jim, it really sounds like one of threethings. Either will require a repair shop.
1. the film sensor is not recognizing film in the film chamber, or film across the back, therefore not telling the advance motor to advance film...
2. The film advance motor itself needs replaced.
3. The rear door latch switch needs replaced.
Since everything else seems to do OK, I doubt the main computer board is bad.

I AM SAGHA REPAIRER FROM MUMBAI I THINK THERE ARE PLENTY OF REASONS SHOWING ERR ON TOP DISPLAY BUT IF ERR IS SHOWING JUST BY TOUCHING THE SHUTTER RELEASE BUTTON THEN THE MAIN BOARD IS DEFECTIVE.IF ANY MECHANICAL ACTION OCCURS AFTER PRESSING SHUTTER RELEASE BUTTON AND THEN ERR APPEARS THEN THE FAULT COULD BE OF SHUTTER & APERTURE BLOCK.I THINK ALL THESE SOLUTIONS ARE FOR EXPERTS AND NOT FOR GENERAL USERS IF ANYBODY FINDS THEM USEFUL LET ME KNOW & ALL THESE ARE BASED ON MY OBSERVATION ABOUT FAULTY CAMERAS.

i have a Orite Mv 3115-Real Dv Mpeg4Vga resolution 30 FPS Digital Veidio Camera. no the problem that the battery of my camera down and i sent that with my friend to bay a new for me unfortunatly he miss that on travel so i need to fins a new battery for that
i hope sir you can healp me to find one and a charger too

rdp19 did not mention the ERR msg.
I had the same problem, however after messing with it the ERR message is up.
If RDP19 gets this, did you get it fixed.  Where and what cost?

1. Turn off the camera.
2. Remove the lens, battery, and CF card.
3. Allow the camera to sit without power for approximately 20 minutes.
4. Insert a fully charged battery, and turn on the camera.
5. Depress the shutter button as you would to take a picture.
Does the “ERR 99′ message appear? If it does, then the camera should be
serviced. If it does not, then please proceed to the next set of steps:
1. Turn off the camera.
2. Insert the CF card.
3. Turn on the camera.
4. Format the CF card in the camera.
5. Depress the shutter button as you would to take a picture.
Does the “ERR 99′ message appear? If so, then the CF card is the most
likely source of the issue. Try using a different card.
If the message does not appear, please complete the following steps:
1. Turn off the camera.
2. Clean the lens contacts by gently rubbing them with a pencil eraser
or soft cloth. Be careful that you do not let any debris fall into the
camera body.
3. Reattach your lens.
4. Turn on the camera.
5. Depress the shutter button as you would to take a picture.
If the “ERR 99′ message only appears when one particular lens is
attached, then that lens should be examined by a service technician.
If you see the “ERR 99′ with a different Canon lens attached, then the
camera should be serviced.

Yes, please turn off the camera when changing lens, make sure on the lens is on its full aperture if you are doing auto. if doest not work to make is test turn the camera on the manual mode and the lens too.
If your lens is new there should not be any problem, if you bought the lens used make sure all the points are clear not rusted. some time when lens fall of it breaks its points inside.

Sounds like the shutter is sticking. This could be due to damage or just need cleaning. This probably means that you need to get the camera professionally serviced/fixed as shutters are extremely delicate.