I'm having this problem as well, but only when I load the SWF containing the TileList with a Loader. I fixed it by adding the TileList component to the library of the Loader's FLA.

absolutezero's solution of adding the class path to the fl.controls folder did not work at all for me.

The guys at Adobe should really be looking at this if they want AS 3 to be a true OO scripting language, but maybe that's what FLEX is for!