Same problem. Found no fix so far. And he says they don't install .jar files as it is unnecessary but I still had one downloaded anyways on the latest version ((that one works but I am recently trying to install an older forge version for older mods) Also not saying he's wrong.I wouldn't know. just posting my experience). But yeh Idk how to fix. : \
Edit: I also found that in another folder only one .jar file was downloaded and is missing the Client and Universal .jar files.