This is a warning, not an error.
Warning: ChopWinding: Rejected(1) due to too many points
A winding is a data structure used in the compile tools to store a set of points. As they are very versatile, they can be used to describe a number of things (surfaces, brush faces, brush sides, whole brushes, etc...). Your warning message is simply alerting you to the fact that one of these winding data structures has a larger number of points than expected, and one of the points was ignored.
It is hard to guess what casues this as most of the typical causes (eg. brush sides with large numbers of vertexes) should be really caught earlier on in the process. Hence, it is most probably the artifact of some subdivision or modification of the points of the map itself during the compile, which makes it even harder to track down. I recommend using the 'Big Block' method of trying to isolate a particular area of your map that causes it, and to modify/simplify/change the general brush geometry. This is a very generic fix, but its also a very generic message.