I'm using Arc10 to try to buffer some polyons (in a shapefile) that I have merged together from separate polygon shapefiles generated in an earlier version of the software. The polys are in GCS (NAD 83), as are the points & lines that I have been working (which have all buffered easily). No matter how I try to buffer the polygons, I get "unknown errors" and "geometry errors" that seem to relate to the XY environment & extent?? I've tried importing the shapefile into a geodatabase & setting the "advanced geodatabase" environment settings in the toolbox before running the buffer command, but I still get the same errors. I've tried projecting the polys into Alber Equal Areas before running the buffer command, but with no more success. Any ideas?
I'd try exporting out to a new shapefile/fc by adding it to ArcMap, right clicking the layer and selecting Data > Export Data. If that doesn't work, try creating a new file gdb and making a new feature dataset using your desired coordinate system and xy domain. Then, try importing the shapefile into it.
P.S. A much easier alternative to all of this seems to be to just use the "select by location" tool on the polygon shapefile, specifying the desired buffer distance as the search distance between the polygons (target layer) and the source layer (intersecting layer).