If I'm posting in the wrong forum please tell me!!!

I've been encoding Dvd's to Avi's using FlaskMpeg (Don't tell me to switch encoder I love it and think it's great ) generally I choose high video quality output such as , high resolution and about 3000 kbps in "DIVX :-)MPEG-4 Low Motion Codec" . I use MicroDvd as my viewing program , recently I'm having some annoying problems I can't solve :
1: Overall video quality is Great and Sharp , BUT , whenever I switch to a 'full screen view' the picture becomes cubic or as if it is behind transparent net ( which creates the cubing effect ) , the problem repeats itself with different viewers ( MediaPlayer , The Playa , etc) but not when I encode using other codecs ( then the picture suck, but no cubing ) so it seems to be a problem of rescaling with this codec
2: Latelly the video became jumpy and motion not fluent .
I've been using the same methods of encoding for more than a year and reasults were allways great and never had any problem so I don't know what cause these problems .
I'd be glad to have any help or refferal to where I can get it , thanks.