Does anyone know what this means and how to fix it?

VirtualDub has dectected an improper VBR audio encoding in the source AVI file and will rewrite the audio header with standard CBR values during processing for better compatibility. This may introduce up to 20894 ms of skew from the video stream. If this is unacceptable, decompress the *entire* audio stream to an uncompressed WAV file and recompress with a constant bitrate encoder. (bitrate: 127.8 +/- 13.1kbps)