Full Screen Resolution Causes Java Binary Error!
You can only play in Windowed Mode. Has been tested numerous times. If you don't want to keep reinstalling play in Windowed Mode until they fix it.
Well then you are one of the few lucky players my friend, cause almost everyone else is having issues with this.

We certainly have something to look into there, but it's not my impression that "almost everyone else" has this same issue.
To anyone else reading this: do post if it's a problem for you or not to get a slight sense of how common it is.
Well my roommate and myself both have the problem. He just had to reinstall again to play.. so.. call me a liar but I just watched him do it.

Are you using Windows 7? I think this may be a bug in the underlying libraries we use.
He uses Windows 7 yes. I use Windows Vista.
I have windows 7 64 bit, and I can run Spiral Knights fine in full screen mode. It's actually prefer playing in full screen.
I can't switch into full mode or change the screen resolution without the game disappearing. I use Windows 7, and my computer passes the minimum system requirements. I tried re-downloading Java and re-installing the game, but neither corrected the problem. I even did the fix listed in the Sticky at the top of the Technical Support section of the forum, which involved changing the value of "display_mode" in the game's registry. The other parts of the options box work fine, such as changing the game's controls. I just cannot change the size of the window or full screen it. Please let me know if there is a fix for this problem.
I am using Windows 7 64-bit. I started having the problem when using full screen mode. I have to reinstall the program to get back into the game.
I have the same problem as Rafiqa, I went to the technical support thing and changed the values in the registry. It helped with the windowed size so I can see it better, however fullscreen still crashes the game. My friend has no problem whatsoever running it in fullscreen, but he also has a macbook.
And by the way I have windows 7 home premium 64-bit
That's a blanket (and incorrect) statement, Prayful. I can play in Fullscreen just fine. In fact, I switch between full and windowed all the time and I've never had to reinstall.