EDIT: Ok so I managed to reproduce that with AC Origins and I discovered the issue was also true for Unity and AC3 Remastered. The games do need to be on Uplay's default game folder. I don't know how on earth something like this can still happen today on games that obviously require loads of storage, and why only on the AC series (all other licenses seem to work just fine) and only on tower PC (no problem on my laptop no matter the drive)?

=> To be tried however: install the launcher on the storage drive

@shenoxdfug super strange then. It definitely solved the problem after full DL, I'll try it with Origins as well, as I had the same issue last week when wanting to run it on my new rig. I'll edit this post if I manage to reproduce this miracle. Also make sure the directory is the default one (setting > downloads > default game intallation location > default) and not manually set, maybe that can help.

EDIT: I uninstalled the game and reinstalled it on my C : drive and it seems to work (download is only partially complete, I'll see what happens when fully DL). Good luck to you guys!

I've got the very same problem. It did the exact same thing when I tried to launch AC Origins on my new PC last week and the support left me on hold since then so no more info I'm afraid. Sad that these are the only two games I wanted to play the most right now, guess I'm gonna go back to Odyssey (which runs just fine for no reason though)... Hope they find us a way to fix that quickly!