Sorenson Squeeze compression causes sound to be not in sync with video

[psaad]

After compressing a .mov file (2GIG) using the following modified preset in Sorenson Squeeze:
.flv VP6_768K_Stream
Frame size: 640x480
Display Aspect Ration Policy: Letter Box
Drop Frames to Maintain Data Rate: 90
--> I also tried with 20 dropped frames and even disabling that features and it still happens

My resulted .flv file's audio and video, when added in a flash file as a new (Actionscript-controlled) video, is not well synchronized.
Its starts synchronized and a few seconds after, the audio is unsynchronized from the video.

This happens when I play the flash file locally, its not even on a web server yet.

If it helps understand my problem:
The original .mov file was generated from an After effects edit I made. I compressed it into a .mov file using the Add to Render Queue, using the Animation preset for the Video Format. I made sure to keep the same fps setting at Medium quality.

But again, this issue does not happen to my original .mov file.

Did anyone encounter that issue when compressing a .mov file into a VP6 flv at 768k stream ? If so, do you know of a way to compress it so that sound and video always stay in sync?

I am using a MacBook Pro 15.4inch
Sorenson Squeeze 4.5.3
Flash CS3

Would appreciate any help possible.

Thanks.

Patrick