You need to uninstall it properly. If not, the problem lies in Java, and you need to update it.

(FOR WINDOWS USERS ONLY)
Having Black Screen issues? Wrong/Weird Images? Or crashes when entering specific areas? See any game errors?
Diagnosis : Corrupted File(s)
Solution : Redownload and Reinstall the WHOLE OF SPIRAL KNIGHTS
FOR STEAM USERS

1. Proceed to Spiral Knights Folder, usually located in C:/Program_Files(x86)/Steam/steamapps/common/Spiral_Knights/
2. Delete this entire folder. The problem is not with the installation, but with the fact that you have corrupted DATA FILES. These data files come to you during downloading, and do not get affected by installation/uninstallation.
3. REDOWNLOAD and REINSTALL the game through the steam store page. Try to ensure smooth and stable download speed, don't go and stream some video, take a break, it's not that long.
4. If problem persists, contact SK support for further inquiries

FOR NON-STEAM USERS

1. Proceed to Spiral Knights Folder. This is possible by starting the "Run" program located in your start menu. Afterwards, key in "%appdata%" to get to the /"User"/Appdata/Roaming / folder. Proceed to /"User"/Appdata/ and access the "LocalLow" folder. There will be a folder called "spiral".
2. Delete this entire folder. The problem is not with the installation, but with the fact that you have corrupted DATA FILES. These data files come to you during downloading, and do not get affected by installation/uninstallation.
3. REDOWNLOAD and REINSTALL the game through the official client page(This website/armorgames/newgrounds, wherever you downloaded it from). Try to ensure smooth and stable download speed, don't go and stream some video, take a break, it's not that long.
4. If problem persists, contact SK support for further inquiries