Oh my oh my, what have you done
the collmaps problem is either because you havent extracted the collmap folder OR it doesnt exist (some trees are meant for show and are not solid)...
the brushes with the "tris with 2+ major axes" is very likely bad brush shaping, or bad cutting or something similar... Use "Misc<find Brush" and type in the numbers of those brushes, they will need to be remade.
node without volumes are going to be your problem. usually a node without a volume is a brush less than 1x1x1 in size. you need to use the coordinates to find and delete those brushes. They may not even be brushes, they could just be flaws. either way the coordinates will direct you to the centre of the problem (you will need to move the camera a little)
and the last error has a fix under it.
hope you get these sorted, in future make sure you are using "snap to grid" (if you are not atm) and careful mapping
