java.lang.NullPointerException in Interferogram Formation

Hi all,

I try to generate a sequential interferograms from sequantial pairs of SLC. First, I create a SLC stack by selecting a common master. Then, I use MultiMasterStackGenerator on the created stack to get a sequence of paired SLCs (For example, the following is one paired SLC).

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At last, I use Interferogram Formation to generate the interferogram from this SLC pair. Then, I got the following error:

java.lang.NullPointerException
at org.esa.s1tbx.insar.gpf.InterferogramOp.computeTileStackForNormalProduct(InterferogramOp.java:886)
Caused: org.esa.snap.core.gpf.OperatorException
at org.esa.snap.engine_utilities.gpf.OperatorUtils.catchOperatorException(OperatorUtils.java:434)
at org.esa.s1tbx.insar.gpf.InterferogramOp.computeTileStackForNormalProduct(InterferogramOp.java:1011)
at org.esa.s1tbx.insar.gpf.InterferogramOp.computeTileStack(InterferogramOp.java:865)
at org.esa.snap.core.gpf.internal.OperatorImageTileStack.computeRect(OperatorImageTileStack.java:122)
at org.esa.snap.core.gpf.internal.OperatorImageTileStack.computeTile(OperatorImageTileStack.java:86)
Caused: org.esa.snap.core.gpf.OperatorException: java.lang.NullPointerException
at org.esa.snap.core.gpf.internal.OperatorExecutor$GPFImagingListener.errorOccurred(OperatorExecutor.java:381)
at com.sun.media.jai.util.SunTileScheduler.sendExceptionToListener(Unknown Source)
at com.sun.media.jai.util.SunTileScheduler.scheduleTile(Unknown Source)
at javax.media.jai.OpImage.getTile(Unknown Source)
at javax.media.jai.PlanarImage.getData(Unknown Source)
at com.bc.ceres.glevel.MultiLevelImage.getData(MultiLevelImage.java:64)
at org.esa.snap.core.gpf.internal.OperatorContext.getSourceTile(OperatorContext.java:449)
at org.esa.snap.core.gpf.internal.OperatorContext.getSourceTile(OperatorContext.java:435)
at org.esa.snap.core.gpf.internal.OperatorImage.computeRect(OperatorImage.java:75)
at javax.media.jai.SourcelessOpImage.computeTile(Unknown Source)
at com.sun.media.jai.util.SunTileScheduler.scheduleTile(Unknown Source)
at javax.media.jai.OpImage.getTile(Unknown Source)
at com.sun.media.jai.util.RequestJob.compute(Unknown Source)
[catch] at com.sun.media.jai.util.WorkerThread.run(Unknown Source)

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Does anyone know what happened? And how to fix this?

Thank you very much!