I thought it was about time to upgrade mencoder, but it fails for me.  What am I doing wrong?

K:\> avs2yuv test0.avs -hfyu test0_huffyuv.avi
test0.avs: 960x720, 50/2 fps, 481 frames
MEncoder 1.0rc2-4.2.1 (C) 2000-2007 MPlayer Team
CPU: Genuine Intel(R) CPU           T2500  @ 2.00GHz (Family: 6, Model: 14, Stepping: 8)
CPUflags: Type: 6 MMX: 1 MMX2: 1 3DNow: 0 3DNow2: 0 SSE: 1 SSE2: 1
Compiled with runtime CPU detection.
Reading from stdin...
success: format: 0  data: 0x0 - 0x0
Cannot seek backward in linear streams!
Seek failed
Cannot seek backward in linear streams!
Seek failed
Cannot seek backward in linear streams!
Seek failed

After these seek messages, it carrys on and appears to be encoding but it produces a zero byte file, then it says:

============ Sorry, this file format is not recognized/supported =============
=== If this file is an AVI, ASF or MPEG stream, please contact the author! ===
Cannot open demuxer.

Exiting...

If I revert to the previous version then it works just fine:

K:\> avs2yuv test0.avs -hfyu test0_huffyuv.avi
test0.avs: 960x720, 50/2 fps, 481 frames
MEncoder 1.0rc1-3.4.2 (C) 2000-2006 MPlayer Team
CPU: Genuine Intel(R) CPU           T2500  @ 2.00GHz (Family: 6, Model: 14, Stepping: 8)
CPUflags: Type: 6 MMX: 1 MMX2: 1 3DNow: 0 3DNow2: 0 SSE: 0 SSE2: 0
Compiled with runtime CPU detection.
Reading from stdin...
success: format: 0  data: 0x0 - 0x0
YUV4MPEG2 file format detected.
YUV4MPEG2 Video stream 0 size: display: 960x720, codec: 960x720
VIDEO:  [YV12]  960x720  12bpp  25.000 fps    0.0 kbps ( 0.0 kbyte/s)
[V] filefmt:12  fourcc:0x32315659  size:960x720  fps:25.00  ftime:=0.0400
Opening video filter: [expand osd=1]
Expand: -1 x -1, -1 ; -1, osd: 1, aspect: 0.000000, round: 1
==========================================================================
Opening video decoder: [raw] RAW Uncompressed Video
VDec: vo config request - 960 x 720 (preferred colorspace: Planar YV12)
VDec: using Planar YV12 as output csp (no 0)
Movie-Aspect is undefined - no prescaling applied.
videocodec: libavcodec (960x720 fourcc=48564646 [FFVH])
Selected video codec: [rawyv12] vfm: raw (RAW YV12)
==========================================================================
New_Face failed. Maybe the font path is wrong.
Please supply the text font file (~/.mplayer/subfont.ttf).
subtitle font: load_sub_face failed.
Writing header...
ODML: Aspect information not (yet?) available or unspecified, not writing vprp header.
Writing header...
ODML: Aspect information not (yet?) available or unspecified, not writing vprp header.

Flushing video frames
Writing index...
Writing header...
ODML: Aspect information not (yet?) available or unspecified, not writing vprp header.

Video stream: 66984.750 kbit/s  (8373093 B/s)  size: 161098316 bytes  19.240 secs  481 frames