problem with netbeans

[Thorsten Kiefer]

Hi,
I opened the j3d-exmples netbeans project.
It contains several classes with main method.
So I opened the properties of the project, go to "build and run".
And under "Run Project" I want to select the class to start.
But the combobox to select the class is disabled. Why ?
How can I reactivate it ?

Best regards
Thorsten