Just a heads up that I managed to solve it but I basically replaced the entire libraries folder with a working copy. Not really a solution that's tackling the issue, just one that's tackling the symptoms so to speak. Basically my install is now a Frankenstein of files.
I have exactly the same issue you're having. Not sure what's going on but it appears that we're not getting the forge client file upon installation of the pack. I guess my computer could be deleting it automatically somehow? I'm going to try downloading the forge files manually...