What works for me is going into task manager, pressing details at the top, selecting the plutonium game (make sure you have the correct one, check by ensuring the one you are selecting has more memory usage on the right) right clicking on it then pressing set priority and high. Gets my crappy old laptop from 7-10 fps to 50-60 on zombies. Don't know about multiplayer though

I have deleted %localappdata%/Plutonium folder and launched plutonium.exe. I am opening the game with plutonium.exe. I have deleted plutonium.exe and downloaded it again. Each time I try to open zombies it comes up with a cmd and then says 'Could not authenticate to Plutonium: snowroller uninitialized'. Switching to LAN and launching the game does work but theres obviously no multiplayer.