Can't import key pair and certificate in KeyStore explorer

• Can't import key pair and certificate in KeyStore explorer with openssl format.
• Error below reported in Keystore Explorer :

org.kse.crypto.CryptoException: Not a valid OpenSSL private key.
    at org.kse.crypto.privatekey.OpenSslPvkUtil.load(OpenSslPvkUtil.java:307)
    at org.kse.gui.dialogs.importexport.DImportKeyPairOpenSsl.loadPrivateKey(DImportKeyPairOpenSsl.java:394)
    at org.kse.gui.dialogs.importexport.DImportKeyPairOpenSsl.importPressed(DImportKeyPairOpenSsl.java:548)
    at org.kse.gui.dialogs.importexport.DImportKeyPairOpenSsl.lambda$initComponents$5(DImportKeyPairOpenSsl.java:270)
    at java.desktop/javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at java.desktop/javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
    at java.desktop/javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
    at java.desktop/javax.swing.DefaultButtonModel.setPressed(Unknown Source)
    at java.desktop/javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
    at java.desktop/java.awt.AWTEventMulticaster.mouseReleased(Unknown Source)
    at java.desktop/java.awt.Component.processMouseEvent(Unknown Source)
    at java.desktop/javax.swing.JComponent.processMouseEvent(Unknown Source)
    at java.desktop/java.awt.Component.processEvent(Unknown Source)
    at java.desktop/java.awt.Container.processEvent(Unknown Source)
    at java.desktop/java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.desktop/java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.desktop/java.awt.Component.dispatchEvent(Unknown Source)
    at java.desktop/java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
    at java.desktop/java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
    at java.desktop/java.awt.LightweightDispatcher.dispatchEvent(Unknown S