Trash quality when encoding long videos with CC?

Hi,

I edited a video in Premiere and the final sequence is about 1 hour long.

When I export this entire sequence to H.264 (Youtube HD 720p 29,98fps - preset from AME), the final output is horrible.

Here is a print screen of it:

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Clik here to view.

With the same settings, I exported only 10 seconds from the sequence, and the quality is nice as it should be:

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Clik here to view.

What's wrong? Anyone could help me?

I'm using the CC version.

Thanks for the help,

Pedro Aquino

www.youtube.com/pedroaquinofx