The object has already been deleted or has not been completely created

Hello,

I'm programming the vmware mangement tool using Java vsphere 5.1 API.

I meet some problem, so, I need your help.

I've got the next error when I power on VMs simultaneously,but VMs actually have been powered on.

"The object has already been deleted or has not been completely created"

I'm using powerOnVMTask() function of VimPortType.

And, I can't create VMs  simultaneously with same error.

" javax.xml.ws.soap.SOAPFaultException: The object has already been deleted or has not been completely created."

I'm using createVMTask() function  of VimPortType.

Can anybody with any knowledge be able to help me?

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I've solved this problem. It was about Java singleton problem -.-;.