Boot from CF fail if USB key is present and EWF enabled

Hello,

I have a XPE system running on CF card with EWF RAM-Reg mode. Everything is
ok, except that, if an USB key is plugged at power on, the system cannot
finish the boot process. It hangs (although the mouse is still active) at
after the welcome screen and never get to the desktop (even if the key is
removed at that moment). If EWF is disabled, there is not this problem. I
have tested different brands of USB key, same result. If the key is plugged
after the boot is finished, XPE can read/write to it without problems.

Thanks in advance for any advice.
--
Ph. Deglon @ R&D Systems SA