I have the same or similar problem.
I make a new imagefile but it's difficult for me to calculate what's the correct size.
But when I flash my COMTREND CT-5361 only I can acces with serial port.
root@OpenWrt:/rom/etc/config# firstboot
Unlocking rootfs_data ...
Erasing rootfs_data ...
[ 8750.516000] jffs2: Too few erase blocks (4)
dmesg
[ 0.300000] bcm963xx_flash: Read Signature value of CFE1CFE1
[ 0.304000] bcm963xx-flash bcm963xx-flash.0: CFE bootloader detected
[ 0.312000] bcm963xx_flash: CFE boot tag found with version 6 and board type 96348GW-11
[ 0.320000] bcm963xx_flash: Partition 0 is CFE offset 0 and length 10000
[ 0.328000] bcm963xx_flash: Partition 1 is kernel offset 10100 and length dff00
[ 0.336000] bcm963xx_flash: Partition 2 is rootfs offset f0000 and length 300000
[ 0.340000] bcm963xx_flash: Partition 3 is nvram offset 3f0000 and length 10000
[ 0.348000] bcm963xx_flash: Partition 4 is linux offset 10000 and length 3e0000
[ 0.356000] bcm963xx_flash: Spare partition is 3c0000 offset and length 30000
[ 0.364000] Creating 5 MTD partitions on "bcm963xx":
[ 0.368000] 0x000000000000-0x000000010000 : "CFE"
[ 0.380000] 0x000000010100-0x0000000f0000 : "kernel"
[ 0.384000] mtd: partition "kernel" must either start or end on erase block boundary or be smaller than an erase block -- forcing read-only
[ 0.404000] 0x0000000f0000-0x0000003f0000 : "rootfs"
[ 0.416000] mtd: partition "rootfs" set to be root filesystem
[ 0.420000] mtd: partition "rootfs_data" created automatically, ofs=3B0000, len=40000
[ 0.428000] 0x0000003b0000-0x0000003f0000 : "rootfs_data"
[ 0.440000] 0x0000003f0000-0x000000400000 : "nvram"
[ 0.452000] 0x000000010000-0x0000003f0000 : "linux"
...
...
The flash size is 4Mb and imagefile openwrt-96348GW-11-gen-squashfs-cfe.bin is 3.713 Kb.
That I see is (may be wrong):
squashfs size is "rootfs" + "kernel" = 3dff00 h = 3967Kb minus overlay
Then overlay jffs2 (rootfs_data) is created with the rest of size: 40000 = 256Kb
3967kb - 256Kb = 3711 Kb (and my file is 3713Kb) -> may be the problem is only 3Kb??
So, what's the problem? may be overlay it's too big? How many "blocks" is needed on overlay partition?
Thanks:
Al9