Firewire drive 'confusion'

I'm embarassed to admit I likely solved this once before, but can't
remember what I did ...

I have an external Firewire housing (older ADS Pyro) that I have installed
a simple EIDE swap bay in -- I have drives that I can insert in the housing
and Windows 2000 SP3 sees them just fine, some smallish 17GB drives, a 40GB
and even a 100GB all without issue.

I also have a swap bay installed in the main case -- and I have drives that
can be opened there too -- the swap bay is the Master on the Secondary.
Again, a range of drives that operate without issue.

What I can't do, and what I'd like to do, is pull a drive from the main
case and swap it to the Firewire housing -- when I try this, in either
direction, the system fails to see the drive, and after endless clicking
(external housing) or completely ignoring (main case) the best I can
achieve is a Windows device manage exclamation point.

Can someone please remind me what I'm doing wrong so that I can swap my
drives between the two bays without remembering which one was in which bay
previously ...

Thanks,
GB
.