improve error messages for "not found"
improve error messages for "not found"

Ignore-this: 4e801d782c33634cde834611ff76e716

darcs-hash:20101025222612-dcabc-9baef97eab33e0da4bc9f6270f139f07248c1a82.gz

phaazon/cuda,phaazon/cuda,phaazon/cuda,mwu-tow/cuda