This would happen if another application is accessing the PCI-324 driver at the same time and you attempt to configure your MOTU Audio interface. If you have the PCI-324 Sound Manager driver enabled for Sound In and Sound Out, and there no applications running besides Digital Performer or Audio Desk but you still get this message, chances are you have an extension enabled that is claiming the Sound Manager driver when the computer boots up. This would be an extension which grabs hold of the sound manager driver when it is loaded at start up.

The solution: Disable the extension or choose Built-In for both Sound In and Sound Out in the Sound Control panel. This does not affect Digital Performer or AudioDesk's use of the MOTU Audio interface. They use the Direct I/O driver located in the MOTU folder, which is found in the Extensions folder. While the PCI-324 driver is a multi-client driver and several applications can access the driver at once, you can not configure the driver while it is in use by another application.