Blockiness in Dark scenes after Decoding!!

[THE DROID]

Can any give me some advice on this matter. I have decoded several avi files into MPEG files without much problems, in fact everyone has turned out just great, except for one small problem. When I view the AVI file that I downloaded in Windows Media player the picture in the dark scenes appears to be smooth, but when I view the MPEG file in the Media player there appears to be white blockiness (pixelling) in the dark scenes, and when you view it on a big 52" screen this is quite noticible. I use TMPGEnc to decode these, could it be that I need to increase the number in "Soften block noise under the Quantize Matrix!!

[TomSem]

try increasing the bitrate or
use CQ VBR in stead of 2 pass VBR