In most cases, at least one duplicate or obsolete entry can be deleted to accommodate Command|8 USB communication by doing the following:
To check the number of MIDI drivers in your
registry:
1 Choose Start > Run.
2 Run “regedit” to display the Windows registry
editor.
3 Expand the HKEY_LOCAL_MACHINE tab.
4 Expand the SOFTWARE tab.
5 Expand the Microsoft tab.
6 Expand the Windows NT tab.
7 Click the Current Version tab.
8 Choose Drivers.32 to display the Drivers.32
tab.
9 Look at the entries in the right hand panel for
MIDI entries listed as “midi” “midi1” and so on.
10 If the highest “midi” entry is 8, then no action
is required. (Skip the following steps and repeat
the software installation steps in “Windows
Software for Command|8” on page 10 to see if
problems persist.)
– or –
If there is an entry for “midi9” then the maximum
number of MIDI drivers has been reached
and at least one must be removed in order for
the Command|8 driver installation to succeed.
To update the number of MIDI drivers in your
registry:
1 Identify any identical (duplicate) entries and
delete the one with the highest entry number.
For example, if there are “rddv1009.dll” entries
in midi3 and midi4, delete the higher one
(midi4).
2 Identify any unused or obsolete entries and
delete them.
3 Repeat the software installation instructions
(see “Installing Software for Command|8” on
page 9).

Taken from the Command8 read me