I developed a plugin ,which extended the struts plugin,I added some wizards in it.But ,after I update the jdk6u17 to 18,it looks like there was some wrong.
yesterday,netbeans can't start,I delete com-tsi-netbeans-modules-languages-velocity.jar in 
C:\Documents and Settings\my username\.netbeans\6.8\modules ,netbeans can start.
because I thought the velocity plugin is wrong,before occur wrong,I update it 2.2.0 to 2.2.1,so I doubt it.But netbeans can't import java.util.Set,java.util.List auto for me,this occured two days ago.so I must reinstall netbeans,I only installed my plugin ,there is no third part others.

Pleanse see the messages.log,

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upgrader_zh_CN.jar
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java.lang.StackOverflowError
	at sun.nio.cs.ext.GBK.newDecoder(GBK.java:32)
	at java.nio.charset.CharsetEncoder.isLegalReplacement(CharsetEncoder.java:311)
	at java.nio.charset.CharsetEncoder.replaceWith(CharsetEncoder.java:267)
	at java.nio.charset.CharsetEncoder.<init>(CharsetEncoder.java:186)
	at java.nio.charset.CharsetEncoder.<init>(CharsetEncoder.java:209)
	at sun.nio.cs.ext.DoubleByteEncoder.<init>(DoubleByteEncoder.java:31)
	at sun.nio.cs.ext.GBK$Encoder.<init>(GBK.java:6786)
	at sun.nio.cs.ext.GBK.newEncoder(GBK.java:36)
	at java.lang.StringCoding$StringEncoder.<init>(StringCoding.java:215)
	at java.lang.StringCoding$StringEncoder.<init>(StringCoding.java:207)
	at java.lang.StringCoding.encode(StringCoding.java:266)
	at java.lang.String.getBytes(String.java:946)
	at java.util.zip.ZipFile.open(Native Method)
	at java.util.zip.ZipFile.<init>(ZipFile.java:114)
	at java.util.jar.JarFile.<init>(JarFile.java:133)
	at java.util.jar.JarFile.<init>(JarFile.java:70)
	at sun.net.www.protocol.jar.URLJarFile.<init>(URLJarFile.java:72)
	at sun.net.www.protocol.jar.URLJarFile.getJarFile(URLJarFile.java:48)
	at sun.net.www.protocol.jar.JarFileFactory.get(JarFileFactory.java:80)
	at sun.net.www.protocol.jar.JarURLConnection.connect(JarURLConnection.java:104)
	at sun.net.www.protocol.jar.JarURLConnection.getInputStream(JarURLConnection.java:132)
	at com.sun.org.apache.xerces.internal.impl.XMLEntityManager.setupCurrentEntity(XMLEntityManager.java:653)
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