CRM Dynamics 2011 Exception Message

Hi,

I would like to ask help in evaluating the exception message i got when saving a record for update context. Please see message details below

"Unhandled Exception: System.ServiceModel.FaultException`1[[Microsoft.Xrm.Sdk.OrganizationServiceFault, Microsoft.Xrm.Sdk, Version=5.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35]]: (Exception) UsageAndExpensePlug-inObject reference not set to an instance of an object.
   at NexusPluginLibrary.UsageAndExpense.Execute(IServiceProvider serviceProvider)
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>
  </ErrorDetails>
  <Message>(Exception) UsageAndExpensePlug-inObject reference not set to an instance of an object.
   at NexusPluginLibrary.UsageAndExpense.Execute(IServiceProvider serviceProvider)
</Message>
  <Timestamp>2014-04-13T11:49:00.0063238Z</Timestamp>
  <InnerFault i:nil="true" />
  <TraceText>

[NexusPluginLibrary: NexusPluginLibrary.UsageAndExpense]
[c1b73b66-3315-e311-87d1-36d7c49cdbe8: NexusPluginLibrary.UsageAndExpense: Update of nexus_usageandexpenses]


</TraceText>
</OrganizationServiceFault>"

I have tried removing all the codes on my update context, rebuild the program and register the plug-in. Yet still i'm getting the same exception message which i assume that i should not experience since i have removed all the codes.

I appreciate any response on this..

Thank you in advance.

Regards,

Honey