Arduino 1.6.4 Sketch not modifiable

Hello, i've a small problem. When i open my "Arduino 1.6.4"-program it starts and i can do anything, but i can't modify the code. I can read the serial commandline or something else. The editfield is grey colored.

|500x409

Hope can help me :)

Regards, Poccix

OS: Microsoft Windows 8.1 Professional x64 Java: Version 8 Update 45 (Build 1.8.0_45-b15)

Found this error:

Exception in thread "AWT-EventQueue-0" java.lang.InternalError: Text component read only