It means Skype has a problem with the device that's selected in Tools > Options > Audio Settings > Speakers.
Go to that setting, pull down the arrow next to the Speakers box, and try selecting any other devices available there.
What devices are showing when you click on the pull down arrow in the Speakers box?
What version of Skype are you running? Click on Help > About Skype for the specific version number.
I would expect the proper choice there would be the top one, "Speaker/Headphones." Do you get the playback device error when selecting that one?
im having the same problem and im using 18.104.22.168
What device do you see selected for Speakers in Tools -> Options -> Audio settings? Is there more than one option available in the selection box? Can you hear any sound when you press the test button next to this selection box?