Unable to access CRM Case customization forms, related workflows and case records even though the users have CRM administrator access.
Tried importing the Case Metadata from another instance but it did not help.

https://XXXXXXXXXXXXXX/_common/error/errorhandler.aspx?BackUri=https%3a%2f%2fmsdcrmtest.allstate.com%2fXXXXXXXXXXXX%2ftools%2fsystemcustomization%2fUIElements%2fforms.aspx%3fentityId%3d%257bE3FE4FF2-A630-49BB-A1E9-DEBC3A076815%257d%26appSolutionId%3d%257bC610A892-C222-4D23-A72F-7B43D7C3219B%257d%26pagemode%3diframe&ErrorCode=&Parm0=%0d%0a%0d%0aError%20Details%3a%20An%20unhandled%20exception%20occurred%20during%20the%20execution%20of%20the%20current%20web%20request.%20Please%20review%20the%20stack%20trace%20for%20more%20information%20about%20the%20error%20and%20where%20it%20originated%20in%20the%20code.&RequestUri=%2fXXXXXXXXXXXX%2fmain.aspx%3fpagetype%3dformeditor%26appSolutionId%3d%257bC610A892-C222-4D23-A72F-7B43D7C3219B%257d%26etc%3d112%26extraqs%3dformtype%253dmain%2526formId%253d4A63C8D1-6C1E-48EC-9DB4-3E6C7155334C%2526action%253d-1&user_lcid=1033
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: #351CCDA8Detail:
<OrganizationServiceFault xmlns:i="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://schemas.microsoft.com/xrm/2011/Contracts">
<ActivityId>ec59f753-3337-41a5-bfba-af915d691662</ActivityId>
<ErrorCode>-2147220970</ErrorCode>
<ErrorDetails xmlns:d2p1="http://schemas.datacontract.org/2004/07/System.Collections.Generic" />
<Message>System.Web.HttpUnhandledException: Microsoft Dynamics CRM has experienced an error. Reference number for administrators or support: #351CCDA8</Message>
<Timestamp>2020-10-16T16:25:38.470559Z</Timestamp>
<ExceptionRetriable>false</ExceptionRetriable>
<ExceptionSource i:nil="true" />
<InnerFault>
<ActivityId>ec59f753-3337-41a5-bfba-af915d691662</ActivityId>
<ErrorCode>-2147220970</ErrorCode>
<ErrorDetails xmlns:d3p1="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: #45D5F6E0</Message>
<Timestamp>2020-10-16T16:25:38.470559Z</Timestamp>
<ExceptionRetriable>false</ExceptionRetriable>
<ExceptionSource i:nil="true" />
<InnerFault i:nil="true" />
<OriginalException i:nil="true" />
<TraceText i:nil="true" />
</InnerFault>
<OriginalException i:nil="true" />
<TraceText i:nil="true" />
</OrganizationServiceFault>