CRM 2013 | Getting error after instrumenting the DLLs

I am trying to do code coverage for .Net. I have instrumented the Dlls using Vsinstr.exe and updated the Dlls using Plugin registration tool. After updating the Dlls with the instrumented Dlls I am getting the below error. I was not getting this error before instrumentation. Can someone let me know what can be the issue after instrumentation of Dlls?

Unhandled Exception: System.ServiceModel.FaultException`1[[Microsoft.Xrm.Sdk.OrganizationServiceFault,

Microsoft.Xrm.Sdk, Version=5.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35]]: An unexpected

error occurred.Detail:

<OrganizationServiceFault xmlns:i="www.w3.org/.../XMLSchema-instance" xmlns="schemas.microsoft.com/.../Contracts">

 <ErrorCode>-2147220970</ErrorCode>

 <ErrorDetails xmlns:d2p1="schemas.datacontract.org/.../System.Collections.Generic" />

 <Message>An unexpected error occurred.</Message>

 <Timestamp>2011-06-07T21:47:31.4167053Z</Timestamp>

 <InnerFault i:nil="true" />

 <TraceText i:nil="true" />

</OrganizationServiceFault>