I have a USA nationwide dataset of wetland polygons and a local polygon layer of parcel. The CONUS wetlands use NAD_1983_Albers, and the parcels use Wa SP N NAD83. Both feature classes use single part geometries. A GIS user (on an older desktop running XP with 1 GB RAM) tried to clip the wetlands to the parcels and got an error message that no polygons were retured. I tried the same tool on my Windows 7 8GB computer (thinking this was a memory issue) and the tool returned a copy of the CONUS wetlands. ?! I manually selected out the CONUS wetlands for my study area and created a new shapefile from that selection, re-ran the clip tool, and everything works fine. No projections were altered in this process. Any thoughts on why this would happen are appreciated.