Why did Sauron fear Aragons coronation?

[Inziladun]

I think that's Peter Jackson "I can make boring 'ol Tolkien better"�™ revision.

In The Two Towers book Aragorn does say that to have realized that an Heir of Isildur was still living "was a blow to [Sauron's] heart".

Sauron naturally would have been shocked to discover that. His attention had been on Minas Tirith for so long that to have such an unexpected revelation threw him into turmoil. He had not forgotten that his previous defeat was at the hands of Isildur, and to have even "his" Palantír, with which he had confused or dominated two of his chief enemies having its link broken to the Orthanc-stone by the Heir filled him with fear. He was mainly worried, I think, that Aragorn would indeed claim the Ring, since in Sauron's mind someone so great could hardly resist it for long. Sauron may have even doubted that he could have recovered it from Aragorn forcibly (though I'm fairly certain he could have).