Error occured when signed message with digital certifcate

Hi,
I am trying to send a rn message but I got an error message -

“java.lang.NullPointerException java.lang.NullPointerException at com.wm.estd.rosettaNet.security.Certificate.createCerChain(Certificate.java:81) at com.wm.estd.rosettaNet.mime.RNSmimeBody.sign(RNSmimeBody.java:280) at com.wm.estd.rosettaNet.mime.RNMimeMessage.sign(RNMimeMessage.java:850)”

when I signed the message with digital certifcate.
can anyone tell me how to solve this error?
thanks in advance!

-------detailed error
java.lang.NullPointerException java.lang.NullPointerException at com.wm.estd.rosettaNet.security.Certificate.createCerChain(Certificate.java:81) at com.wm.estd.rosettaNet.mime.RNSmimeBody.sign(RNSmimeBody.java:280) at com.wm.estd.rosettaNet.mime.RNMimeMessage.sign(RNMimeMessage.java:850) at com.wm.estd.rosettaNet.rnif20.mime.RNIF20Message.(RNIF20Message.java:93) at com.wm.estd.rosettaNet.rnif20.RNIF20Transport.send(RNIF20Transport.java:275) at com.wm.estd.rosettaNet.RequestHandler.send(RequestHandler.java:1216) at wm.estd.rosettaNet.transportHandlers.send(transportHandlers.java:384) at sun.reflect.GeneratedMethodAccessor676.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:592) at com.wm.app.b2b.server.JavaService.baseInvoke(JavaService.java:403) at com.wm.app.b2b.server.invoke.InvokeManager.process(InvokeManager.java:631) at com.wm.app.b2b.server.util.tspace.ReservationProcessor.process(ReservationProcessor.java:40) at com.wm.app.b2b.server.invoke.StatisticsProcessor.process(StatisticsProcessor.java:44) at com.wm.app.b2b.server.invoke.ServiceCompletionImpl.process(ServiceCompletionImpl.java:241) at com.wm.app.b2b.server.invoke.ValidateProcessor.process(ValidateProcessor.java:51) at com.wm.app.b2b.server.ACLManager.process(ACLManager.java:228) at com.wm.app.b2b.server.invoke.DispatchProcessor.process(DispatchProcessor.java:30) at com.wm.app.b2b.server.AuditLogManager.process(AuditLogManager.java:624) at com.wm.app.b2b.server.invoke.InvokeManager.invoke(InvokeManager.java:536) at com.wm.app.b2b.server.invoke.InvokeManager.invoke(InvokeManager.java:381) at com.wm.app.b2b.server.ServiceManager.invoke(ServiceManager.java:237) at com.wm.app.b2b.server.BaseService.invoke(BaseService.java:189) at com.wm.lang.flow.FlowInvoke.invoke(FlowInvoke.java:324) at com.wm.lang.flow.FlowState.invokeNode(FlowState.java:581) at com.wm.lang.flow.FlowState.step(FlowS…