Kindle app variable behaviour in iPad & Mac Book Air-Snowleopard OS?

My iPad iOS 5.1.
My Mac Book Air has the latest Snow Leopard OS.

I have downloaded the kindle app on both the iPad & Mac Book Air.

At the time of the kindle App download to install, I used the same Amazon e-mail address to register my kindle App.

In my kindle account I have included my personal e-mail address to enable me send my personnal pdf files, that would allow me to store and open my pdf files in my Kindle Apps either in the iPad or Mac Book Air.[I thought I could do]

I am able to open the pdf file in my iPad Kindle app but not in my Mac Book Air Kindle App?
I went into my "Manage your Kindle Account" in Amazon where to include other devices or the allow personal Documents.

I could see my personal Documents and in "Actions" drop down Menu- "Deliver to my .....

Here in "Deliver to my .....
Deliver to : both are there my iPad name and my Mac Book Air name but the Mac Book Air is greayed out and I could not select it to be delivered to Mac Book Air??

Is there any way I could open my personal document on both devices in my Kindle App that is registered to one and the same Amazon account?

Thanking you for your advice.