When you use the DiskPart public domain Resource Kit tool to create virtual drives on a dynamic disk, you receive an error message when all 26 drive letters have been used.

To avoid this problem, use a script similar to:

Select disk 1
create vol
remove
detail vol

NOTE: the remove command must immediately follow the create vol command.

NOTE: When you type diskpart /?, you receive:

Microsoft DiskPart version 5.1.3553
Copyright (C) 1999-2001 Microsoft Corporation.
On computer: <ComputerName>

Microsoft DiskPart syntax:

        diskpart \[/s <script>\] \[/?\]

        /s <script> - Use a DiskPart script.
        /?          - Show this help screen.
NOTE: After installing Diskpart, the documentation is available at "%ProgramFiles%\Resource Kit\DISKPART_D.HTM".