This can also happen if you have multiple audio devices. I use a Behringer U-Phoria external audio device. I was having problems with that error until I disabled my laptops onboard Realtek audio device.
Yes. I get the error if I try to have Finale open with a browser, Windows media player, VLC, or other audio software open at the same time. Clicking the Mono button seems to reset something so it all works.
Some audio devices can claim exclusive control of the computer or external sound card. Check your device drivers (at the system level as well as any program specific configuration panels) to make sure this is not happening.
I had this problem (error 7) upon FINALE startup after plugging in my Yamaha keyboard and working successfully the night before (might or might not be related). I solved the problem by unplugging my accessory camera/microphone from an adjacent USB port and restarting FINALE.