I've had this problem twice before. The first time I finished playing a co-op campaign, and when I tried to launch shogun 2 later that day all the sekigahara campaign mod files I had been using in the co-op campaign were gone. The second time this happened I was playing a single player campaign the data file was gone. Both times shogun 2 wouldn't launch and I had to re-download some of the files. Has this happened to anyone else and why does it happen to me?