Unable to Delete Work Hours From a User Account in CRM, getting exception. For few System Users.

Hi Experts,

Following error is coming out for some random users. Like some users are unable to update/delete workhours.

Is there any approach to compare the delta with users which are not getting issue, I tried compare associated tables not didn't find any clue ?

Following is the Exception message is coming while deleting the Workhours.

Unhandled Exception: System.ServiceModel.FaultException`1[[Microsoft.Xrm.Sdk.OrganizationServiceFault, Microsoft.Xrm.Sdk, Version=8.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35]]: System.Web.HttpUnhandledException: Microsoft Dynamics CRM has experienced an error. Reference number for administrators or support: #071C6B97Detail: 

<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>System.Web.HttpUnhandledException: Microsoft Dynamics CRM has experienced an error. Reference number for administrators or support: #071C6B97</Message> 
<Timestamp>2017-07-06T17:17:03.9446079Z</Timestamp> 
<InnerFault> 
<ErrorCode>-2147220989</ErrorCode> 
<ErrorDetails xmlns:d3p1="schemas.datacontract.org/.../System.Collections.Generic" /> 
<Message>This operation isn't supported</Message> 
<Timestamp>2017-07-06T17:17:03.9446079Z</Timestamp> 
<InnerFault i:nil="true" /> 
<TraceText i:nil="true" /> 
</InnerFault> 
<TraceText i:nil="true" /> 
</OrganizationServiceFault> 

Can anybody please help me to know what is causing the error.

Thanks

Shubh