So you're definitely using 1.0. My first thought is to switch to 1.1, if you can.
If you can't, then my next thought is that the times that you're seeing this error, your code is not returning a CFC (which would be done using representationOf()...)
I would expect this to happen if you had:
return "foo";
instead of:
return representationOf( "foo" );
... does that make sense?
Adam