Plugin Business process error

Hi All,

We are creating opportunity on click of custom button in lead using plugin. 

 var qualifyIntoAccountContactReq = new QualifyLeadRequest
                        {
                            CreateAccount = true,
                            CreateOpportunity = true,
                            CreateContact = true,
                            LeadId = new EntityReference("lead", entity.Id),
                        };

Getting bellow error while doing so

Unhandled Exception: System.ServiceModel.FaultException`1[[Microsoft.Xrm.Sdk.OrganizationServiceFault, Microsoft.Xrm.Sdk, Version=6.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35]]: An error occurred in the Plugin.System.ServiceModel.FaultException`1[Microsoft.Xrm.Sdk.OrganizationServiceFault]: An unexpected error occurred. (Fault Detail is equal to Microsoft.Xrm.Sdk.OrganizationServiceFault).Detail: 
<OrganizationServiceFault xmlns:i="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://schemas.microsoft.com/xrm/2011/Contracts">
  <ErrorCode>-2147220891</ErrorCode>
  <ErrorDetails xmlns:d2p1="http://schemas.datacontract.org/2004/07/System.Collections.Generic">
    <KeyValuePairOfstringanyType>
      <d2p1:key>OperationStatus</d2p1:key>
      <d2p1:value xmlns:d4p1="http://www.w3.org/2001/XMLSchema" i:type="d4p1:string">0</d2p1:value>
    </KeyValuePairOfstringanyType>
    <KeyValuePairOfstringanyType>
      <d2p1:key>SubErrorCode</d2p1:key>
      <d2p1:value xmlns:d4p1="http://www.w3.org/2001/XMLSchema" i:type="d4p1:string">-2146233088</d2p1:value>
    </KeyValuePairOfstringanyType>
  </ErrorDetails>
  <Message>An error occurred in the Plugin.System.ServiceModel.FaultException`1[Microsoft.Xrm.Sdk.OrganizationServiceFault]: An unexpected error occurred. (Fault Detail is equal to Microsoft.Xrm.Sdk.OrganizationServiceFault).</Message>
  <Timestamp>2015-09-30T04:33:14.5886888Z</Timestamp>
  <InnerFault i:nil="true" />
  <TraceText>
[LeadQualify:LeadQualify.qualifyLead]
[9c0eb808-f765-e511-80cd-a95511b30fc0:LeadQualify.qualifyLead: Update of lead]
</TraceText>
</OrganizationServiceFault>

Can any one suggest me to resolve this issue. 

Thanks.