Hey Viper
Just a thought, double check and make sure the (correct version, as Silent1 said) PBO's are directly in your Addon's folder and not inside another folder within Addons.
I had the same problem with the Gimbal planes, when I extracted the files, another folder was created within my AddOns folder and I had to move the PBO's out from that folder into my Addon's folder.
(thinks hard)
I can't say that I remember the same thing happening with the LittleBirds but I'm not sure.
.....and since we're talking about BAS' artistry, be sure to download the Delta/Ranger pack as well as the new Chinook!!
You won't regret it!!!
(Marvin is in NO WAY affiliated with Ballistic AddOn Studios) although he would jump at the chance to be.......