Shutter Release not working sometimes - Lens Problem - HELP!!

Hi Everyone,

I am a professional photographer with a problem that I have never had happen before and I'm hoping you can help me. I have a D300 with a 28-70 lens that is having problems with the shutter release. I have diagnosed it down to the lens as other lenses work fine on my D300 and I have tried the lens on my D200 and D100 and I have the same problem with the lens. Just wanted you to get off to the right start as far as helping me diagnose. By the way, I really appreciate your even reading this and hopefully you will have some insights for me.

The problem...The camera will pre-focus SOME of the time but even if it does focus, when I press the shutter button down the rest of the way, it does not take the picture. On the times when it won't focus, if I turn the manual focus ring on the lens, then pre-focus, it will pre-focus but again, will not take the picture.

Is there anything I can do. I REALLY don't want to have to send it in for repair if there is something I can do. I have already tried to clean the contacts and checked the screws to make sure they weren't loose but besides that, that's all I've done.

Look forward to your insights.