Community
I don't know if this will help anyone, but we have been having trouble with sheetsets becoming invalid. It started when we updated some computers to 64 bit. It seems to happen when two computers with different operating systems open the sheetset. My dst file went from 65kb to 0kb. I found out (by accident) that when I deleted to invalid sheetset (0kb) it would come back to life as a 65kb...no problems. I've been keeping the older computers away from the sheetsets until we can convert the office or until Autodesk comes up with a patch.
Mark Green
Working on Civil 3D in Canada