Ошибка Audio upmixing is not available в Adobe Premiere Pro 2.0

переконвертируйте свой мпег в DV, родной формат премьера.
и будет Вам Щязтье :)

update: не поленился, залез на сайт Адобов, вот что они пишут

Issue

When you export a Premiere Pro project through the Adobe Media Encoder, Premiere Pro returns the error message, "Audio Upmixing is not allowed. Cancelling the operation."

Detail

The destination audio format contains more audio channels than the master track of your Premiere Pro sequence.

Solution

Do one or more of the following solutions:

Solution 1: Choose a different audio export setting.

Change your audio settings in the Adobe Media Encoder to match the number of channels used in the Master audio track of your Premiere Pro sequence. For example, if you have a Stereo Master audio track in your Premiere Pro sequence, then select a preset in the Adobe Media Encoder that is also Stereo.

Solution 2: Nest your Premiere Pro sequence into a new sequence with the proper number of audio channels.

If your Premiere Pro sequence has fewer channels than your intended export setting, then you can add your sequence to a new sequence with the proper number of audio channels in the Master audio track.

To create a new sequence with the proper number of Master Audio channels:

1. Choose File > New > Sequence.

2. Under Audio, choose a Master setting that reflects your intended output (Mono, Stereo, or 5.1), and click OK.

You can now drag your original sequence from the Project panel to the new sequence you created.

Solution 3: Use the SurCode Encoder. (MPEG2 only)

If your intended output is MPEG2, then you can use the trial version of the SurCode Encoder that is installed as a part of Adobe Premiere Pro.

Note:The SurCode Encoder is available on a trial basis only. After three (3) uses you must purchase the full version in order to continue using the Encoder.

Видимо тот формат в который вы сохраняете, а точнее стандарт, не поддерживает хар-ки вашего исходника. Проверяйте весь свой материал, чтобы был не разношерстный и подходил под стандарт.

gutalin все правильно вам ссылку привел, выводите в нормальном формате, т. е. АС3 и все будет пучком.
http://www.capture.ru/adobe/premiere_22.html