Rockbox

I am trying to use the last method mentioned on the ipodpatcher wiki page to write Rockbox directly into the OSOS image on my iPod Nano2G. Sometimes it works properly, but other times it fails saying that it couldn't read the header from the .ipodx file. I am following the instructions exactly, so that can't be an issue. I have tried hexediting the .ipodx file, and in some cases I can get ipodpatcher to read the header by editing the first four values, but this always causes a Checksum Error. Here is the exact output:

C:\Users\Michael Marley\Downloads>ipodpatcher.exe -wf rockbox.ipodx
ipodpatcher 5.0 with v4.0 bootloaders (v1.0 for 2nd Gen Nano)
(C) Dave Chapman 2006-2009
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

[INFO] Scanning disk devices...
[INFO] Read XML info (4 bytes)
[INFO] Ipod found - 2nd Generation Nano ("winpod") - disk device 1
[INFO] Reading partition table from \\.\PhysicalDrive1
[INFO] Sector size is 2048 bytes
[INFO] Part Start Sector End Sector Size (MB) Type
[INFO] 0 63 48194 94.0 Empty (0x00)
[INFO] 1 48195 1982462 3777.9 W95 FAT32 (0x0b)
[INFO] Read XML info (4 bytes)
[INFO] Ipod model: 2nd Generation Nano ("winpod")
[ERR] Failed to read header from rockbox.ipodx
[ERR] --write-firmware failed.