What i see right away is the raster iterator.
have you tried using the Iterate files instead?
it reads files in a folder and can push that file to a tool, such as the ascii to raster tool
Tried all of the iterators, none will link as an input. The "Iterate Files" specifically only has the option to set itself as the precondition to the ASCII tool.
Strange.. I just tried to make the iterators connect to the ascii 3d tool, no problem, immediately connected as input.
I don't know what would be wrong,
have you updated to the latest SP?