Win 7 64-bit, DF Pro v9.3

I'm using my laptop with 3 external monitors (so 4 screens in total). I have a monitor profile for when all 4 screens are enabled ("4_screens"). I wanted to modify this setup to disable the laptop screen and then save that as a new profile.

In the Monitor Configuration window, when I select the laptop screen, then select Disabled from the drop-down menu, and then select Apply, I receive the following error message:

An error has occurred while applying your new Monitor configuration.
Please check your settings and try again.
Error: Failed to call EnableMonitors.

As an attempted workaround, I used Windows' screen resolution menu to disable the laptop screen, then went into DF and saved the configuration as a monitor profile ("3_screens"). When I attempt to switch profiles from "4_screens" to "3_screens", I receive the same error message.

Any ideas on what's causing this?