Can't boot from USB stick with CDROM+HDD

[mage]

Hello!

I have a USB stick with 2 LUN. LUN0 = USB-CDROM with grub4dos (Hiren's BootCD), LUN1 = USB-HDD with grub4dos in MBR (multiboot), i.e. BIOS & Windows detect it as 2 different devices. On desktop computer everything works ok, I can boot from both.
Problems appeared with new HP laptop - BIOS doesn't show USB-HDD in any configuration. CDROM boots ok, Windows detects both.
I tried to use PLOP to boot USB-HDD, but failed.
Boot process: USB-CDROM->Grub4dos->PLOP->USB... stop. PLOP detects 2 USB devices, tries to boot and reports "No HD".
Where is a problem with PLOP (or with my config)? Why it can't find & boot from LUN1? How can I get detailed (debug) info on USB boot process in PLOP?

[Elmar]

maybe there is a internal usb hub.

regards
elmar

[mage]

May be. Device Manager shows 2 USB Root Hub with some devices (bluetooth, webcam, etc.). PLOP doesn't support it?

Mage

[Elmar]

what operating system do you want to boot from usb?

[mage]

Windows & Linux via grub4dos bootloader (multiboot).