Hi, I got the same error, so I started to invent and I noticed that it works if you go to the audio folder and look for the skill1.ogg file and just make a copy of the skill1.ogg file, just change the name from skill1.ogg to skill2.ogg and you will notice that the game should start working fine.
thanks for the help! Though just incase I realized it's suppose to say "Skill2.ogg_" with the underscore at the end otherwise it would turn into a media player.
