A couple things here to try and confirm, so we'll know where you're at. This may be the same stuff you've done, but we've got to establish a base line.
1.) When you downloaded the All in Arma Terrain Pack, did you ensure that you downloaded the Full Pack (largest filesize), and not the lite? Did you also ensure that you downloaded the hotfix and AiA update? Did you copy those pbo's straight into your AiATP pack?
2.) No clue what that's in reference to.
3/4.) There is a certain order that some of the mods need to be installed in. You must install the RHS BEFORE installing the 506th pack RHS pbo's. Otherwise it will overwrite them, and you'll be missing some pretty important stuff.
Have you any other mods, other than what's required for the 506th, installed and running? If you do, you may wish to turn them off, and see if the same errors occur.