Define the error message which was used at quite a few places but never defined.
Define the error message which was used at quite a few places but never defined.

--HG--
extra : rebase_source : 6c32f6a8771a729a15724f4b9237bdb1174edfd1

rhyolight/nupic.son,rhyolight/nupic.son,rhyolight/nupic.son