Error message - Could'nt read YUV4MPEG header

[LoafingOaf]

Hi Folks! I'm wondering if someone could assist me with this rather strange issue. All of a sudden I'm getting this same error message almost initially on commencing encoding for any file I care to attempt conversion on. All avi's being converted to DVDs using mpeg2enc. I need to use mpeg2enc because they all have subtitles, and the default Pos for subtitles using ffmpegx is 80 and uneditable for some weird reason, and that puts them way too far up the screen. This has been my standard methodology for aeons and all of a sudden I'm getting error messages as follows. The only thing which has been out of the ordinary was several failed attempts to convert a large (1.4Gig) MP4 file which I aborted after it literally running for about three days and appeared stuck at about 55%. I thought perhaps it might be a problem with the binaries, but they all seem to be fine. Any assistance greatly appreciated!

INFO: [yuvscaler] yuvscaler 1.9.0 (15-02-2004) is a general scaling utility for yuv frames
Sat May 29 06:27:22 EST 2010
INFO: [yuvscaler] (C) 2001-2004 Xavier Biquard <xbiquard@free.fr>, yuvscaler -h for help, or man yuvscaler
INFO: [mpeg2enc] SETTING AltiVec for MOTION!
INFO: [mpeg2enc] SETTING AltiVec for TRANSFORM!
INFO: [mpeg2enc] SETTING AltiVec for PREDICTION!
movtoy4m
Copyright 2002-2006 Johan Lindström
All rights reserved..
**ERROR: [yuvscaler] Could'nt read YUV4MPEG header!
**ERROR: [mpeg2enc] Could not read YUV4MPEG2 header: system error (failed read/write)!

[Case]

Can you post the codec details for this problematic AVI?
Which decoder is selected in the Options tab (QuickTime, mplayer, neither (= ffmpeg)) ?
If 'Decode with Quicktime' is selected, do you have Perian installed?