org.pentaho.di.core.exception.KettleException:java.lang.IllegalArgumentException: key

Hi
all of sudden when i open spoon.bat i am getting following error message in console.

DEBUG: Using JAVA_HOME
DEBUG: _PENTAHO_JAVA_HOME=C:\Apps\java\jdk1.6.0_45
DEBUG: _PENTAHO_JAVA=C:\Apps\java\jdk1.6.0_45\bin\java
on "C:\Apps\java\jdk1.6.0_45\bin\java"
log4j:WARN Continuable parsing error 11 and column 69
log4j:WARN Document root element "log4j:configuration", must match DOCTYPE root
"null".
log4j:WARN Continuable parsing error 11 and column 69
log4j:WARN Document is invalid: no grammar found.
2016-07-20 11:27:10,115 [main] org.apache.commons.vfs.impl.StandardFileSystemMan
ager INFO - Using "C:\Users\KALANI~1.GUR\AppData\Local\Temp\vfs_cache" as temp
orary files store.
java.util.concurrent.ExecutionException: java.lang.IllegalArgumentException: key
can't be empty
at java.util.concurrent.FutureTask$Sync.innerGet(FutureTask.java:222)
at java.util.concurrent.FutureTask.get(FutureTask.java:83)
at org.pentaho.di.ui.spoon.Spoon.main(Spoon.java:611)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.
java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAcces
sorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.pentaho.commons.launcher.Launcher.main(Launcher.java:151)
Caused by: java.lang.IllegalArgumentException: key can't be empty
at java.lang.System.checkKey(System.java:774)
at java.lang.System.setProperty(System.java:722)
at org.pentaho.di.core.util.EnvUtil.environmentInit(EnvUtil.java:115)
at org.pentaho.di.core.KettleClientEnvironment.init(KettleClientEnvironm
ent.java:76)
at org.pentaho.di.core.KettleEnvironment.init(KettleEnvironment.java:91)


at org.pentaho.di.core.KettleEnvironment.init(KettleEnvironment.java:69)


at org.pentaho.di.ui.spoon.Spoon$1.call(Spoon.java:569)
at org.pentaho.di.ui.spoon.Spoon$1.call(Spoon.java:562)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExec
utor.java:895)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor
.java:918)
at java.lang.Thread.run(Thread.java:662)


C:\Apps\pdi-ce-5.1.0.0-752\data-integration>



can anyone help us on this.

even i taken the new version pdi 6.1. but no luck again i am getting same error.

Thanks
Kalanidhi