Strange error when trying to create opportunity, user is System Admin

I have a user who is also a System Administrator. They are receiving the following error when trying to create a new opportunity record. The error appears after the user selects a contact or an account in the appropriate fields. The system allows the user to select from the vLookup, but then doesn't allow the user to save the opportunity.

I don't read code and have no idea how to interpret this.

Unhandled Exception: System.ServiceModel.FaultException`1[[Microsoft.Xrm.Sdk.OrganizationServiceFault, Microsoft.Xrm.Sdk, Version=5.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35]]: System.NullReferenceException: Microsoft Dynamics CRM has experienced an error. Reference number for administrators or support: #81F4ED42Detail: 

<OrganizationServiceFault xmlns:i="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://schemas.microsoft.com/xrm/2011/Contracts">

  <ErrorCode>-2147220970</ErrorCode>

  <ErrorDetails xmlns:d2p1="http://schemas.datacontract.org/2004/07/System.Collections.Generic" />

  <Message>System.NullReferenceException: Microsoft Dynamics CRM has experienced an error. Reference number for administrators or support: #81F4ED42</Message>

  <Timestamp>2016-02-16T16:26:28.0629391Z</Timestamp>

  <InnerFault i:nil="true" />

  <TraceText i:nil="true" />

</OrganizationServiceFault>