Puzzled with SCSI drives

We have the strangest of problems that we were trying to investigate for
a long time, without any clue.

We have one XPE image that we're deploying onto our PC model. Some of the
manufactured PCs contain a SCSI controller card, and external SCSI
harddisk drives are attached. The drivers are included with the image.

Under certain conditions (which I will describe later), the following
symptom shows: Windows comes up (WinLogon), and you can try to log on.
But then the desktop isn't being shown, and a message box comes up "A
problem is preventing Windows from accurately checking the license for
this computer. Error code: 0x80090006", or: "

(I know that "Error code 0x80090006" can occur if the boot partition
size isn't set correctly in TD. This is not the case.)

The strange thing is: This only happens under certain conditions, in
particular:

VARIATION 1:

1) SCSI card not built in
2) XPE image deployed
3) card still not built in
4) first start of XPE, and shutdown
5) card built in, disk connected and switched on
6) second start of XPE
ERROR OCCURS (for this and every following attempt)

VARIATION 2:

1) SCSI card built in, disk connected but switched off
2) XPE image deployed
3) disk still switched off
4) first start of XPE, and shutdown
5) disk switched on
6) second start of XPE
ERROR OCCURS (for this and every following attempt)

VARIATION 3:

1) SCSI card built in, disk connected but switched off
2) XPE image deployed
3) disk switched on
4) first start of XPE, and shutdown
5) disk still switched on
6) second start of XPE
ERROR DOES *NOT* OCCUR (neither with any following attempt),
WINDOWS STARTS REGULARLY

The problem is absolutely independent from disk or SCSI controller
manufacturers, we tried several combinations.

The behaviour causes us big trouble because we would have to manufacture
*every* PC (initially meant with SCSI or not) with "Variation 3" in order
to make sure it can be upgraded to SCSI at a later time. Also, we would
very much like to understand what the BEEP is going on.

If you need further details, I'll be very glad to give them. I'm really
at a loss here.