When open netbeans and press run on a project it throws

D:\Workspace\DocSamples\UIControlSamples\nbproject\build-impl.xml:87: The J2SE Platform is not correctly set up.
 Your active platform is: default_platform, but the corresponding property "platforms.default_platform.home" is not found in the project's properties files.
 Either open the project in the IDE and setup the Platform with the same name or add it manually.
 For example like this:
     ant -Duser.properties.file=<path_to_property_file> jar (where you put the property "platforms.default_platform.home" in a .properties file)
  or ant -Dplatforms.default_platform.home=<path_to_JDK_home> jar (where no properties file is used)

I got only one java platform in netbeans which is default. I used netbeans 7.4 beta.