TPL in Custom workflow in mscrm 2011

Hi,

I am using  TPL  approach for creating task in mscrm 2011 workflow . Sometimes i am getting Invalid operation error

{System.ServiceModel.FaultException`1[Microsoft.Xrm.Sdk.OrganizationServiceFault]: System.InvalidOperationException: Microsoft Dynamics CRM has experienced an error. Reference number for administrators or support: #B7267DE8 (Fault Detail is equal to Microsoft.Xrm.Sdk.OrganizationServiceFault).}

Sometimes  database related error as descibed below,Is  Multithreading allowed in custom workflow?

Abhishek