Error:Audio upmixing not allowed

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."

Solutions

 * See Aodbe Technical Support Document 332333
 * A quick fix is to create a new sequence with a master stereo audio track to contain your other sequences, and export the new sequence.