GRUB SYSLINUX booting from logical partiton on USB drive

[greenfinch]

Hello,

I cannot boot with GRUB (grub-0.97-r4) and SYSLINUX (syslinux-3.63) from 
a logical partition
on my USB drive.

Here is the test setup:

- 4GB Flash drive with the following partitions:

sdb1   Primary fat32 ~ 800MB
sdb2   Primary fat32 ~ 800MB
sbd3   Primary fat32 ~ 800MB
sdb4   Extended partition
sdb5   Logical partition ~ 800MB
sdb6   Logical partition ~ 600MB

- Grub files were copied to /dev/sdb1/boot/grub (Stage files, etc.)
- Grub was installed in the MBR of the USB flash drive.
- Damn Small Linux (DSL) was downloaded an unzipped to the root of sdb5 
(zip-file dsl-4.2.5-embedded)
- sdb5 was made bootable by:    syslinux -sf  /dev/sdb5    (SYSLINUX 
version 3.63)
- Now the USB flash drive is bootable
- After reset, the grub prompt appeared, and I tried to boot from sdb5:

root (hd0,4)
rootnoverify (hd0,4)
chainloader --force (hd0,4)+1
boot
Boot error

---
My question is, why there is the boot error?
I've successfully tried the following:
- Booting DSL from sdb1, sdb2, sdb3 without any problems -> OK.
- Booting a 2nd GRUB, installed in the logical partition sdb5 -> OK.
- Booting DSL installed on sdb5, by using the kernel/initrd-booting of 
GRUB (without chainloader)

Where is the limitation?
Is is SYSLINUX or GRUB?
Maybe someone can help me to be able to chainload SYSLINUX from an 
logical partition.

Thank you for your answer.

greenfinch