I had Spiral Knights installed for a while bit I didn't play it for a long time. When I started it up, nothing happened so I started it up again. A small window came up saying that another instance was running and that it would close and let the other one finish and it said 0%. Nothing ever happened and couldn't get the game to get past that so I deleted it from steam and re-downloaded it.
Now when I try to start up Spiral Knights in steam, a small window comes up saying downloading data. When it finishes, it says validating. When that finishes, it goes back to downloading. Eventually it fails after 5 times.
AMD Athlon II P360 Dual-Core 2.3 GHz
4GB Ram
Windows 7
ATI Mobility Radeon HD 4250
I would try to completely uninstall the game first via the delete local content option on Steam and then go into your Steam folder and make sure Spiral Knights folder is empty. Then install the game from Steam like normal.
It sounds like you are having a issue patching that is supposedly fixed, so perhaps a fresh start will help things.