Insufficient Permission error for a User with System Administrator role

A very strange issue indeed. We are using CRM 2013 On-Prem and I was trying to assign an Account record to another user. The user I am logged in as is the CRM admin (with system administrator privileges). The same user who installed CRM 2013.

However, I am receiving Insufficient Permissions error when trying to assign an Account record to another user. Here is the error log:

Unhandled Exception: System.ServiceModel.FaultException`1[[Microsoft.Xrm.Sdk.OrganizationServiceFault, Microsoft.Xrm.Sdk, Version=6.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35]]: System.Web.HttpUnhandledException: Microsoft Dynamics CRM has experienced an error. Reference number for administrators or support: #56C416D8Detail:
  -2147220970
  System.Web.HttpUnhandledException: Microsoft Dynamics CRM has experienced an error. Reference number for administrators or support: #56C416D8
  2014-11-13T07:29:15.5961334Z
    -2147220960
    Principal user (Id=3d3d03f5-f73e-e311-b67b-002219609c15, type=8) is missing prvReadContract privilege (Id=8022a167-ea97-4c91-a41c-b77c083f7113)
    2014-11-13T07:29:15.5961334Z

Solutions

At first I was baffled as I am logged in as System Administrator and how can I not have the privileges however, this is how I resolved it.

Focus on the tag in the error log above. The Principal User ID is '3d3d03f5-f73e-e311-b67b-002219609c15'

I searched for this ID in SystemUserBase table in SQL Server.

SELECT * FROM SystemUserBase WHERE SystemUserId LIKE '3d3d03f5-f73e-e311-b67b-002219609c15'

When I reviewed the details of this record, it wasn't the System Admin but the Target User to which I was assigning this record to.

I checked his Role in CRM (Setting / Administration / Security Roles) and provided him read privileges for Contracts entity (prvReadContract privilege as mentioned in the error above).

The error was resolved and the Account record now had a new Owner.