[Fox Lee]

My group had a lot of this. It seems to be an error with duplicate things that are in both the downloaded DDI files and the new community-made files (and the various patches available, if you have any of those).

If memory serves, we fixed it by deleting all the DDI .user files entirely. I recommend moving the files mentioned in that error message into a temporary folder, far away from HL, and seeing if it will work then (that way, you can always move them back if it gets worse!).