I am adding the log file details. Looks like there is a custom workflow, that is giving this error. I need to check the workflow now, what is it doing?
Anyways posting the error log
Unhandled Exception: System.ServiceModel.FaultException`1[[Microsoft.Xrm.Sdk.OrganizationServiceFault, Microsoft.Xrm.Sdk, Version=7.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35]]: User with ID 6911f700-68b5-e711-80dd-00155da70437 does not have Update permissions for the erm_delegatetouser attribute in the erm_delegation entity. The erm_delegationid of the record is 7e3790f9-75bd-e711-80e8-00155da70437Detail:
<OrganizationServiceFault xmlns:i="www.w3.org/.../XMLSchema-instance" xmlns="schemas.microsoft.com/.../Contracts">
<ErrorCode>-2147220891</ErrorCode>
<ErrorDetails xmlns:d2p1="schemas.datacontract.org/.../System.Collections.Generic">
<KeyValuePairOfstringanyType>
<d2p1:key>CallStack</d2p1:key>
<d2p1:value xmlns:d4p1="www.w3.org/.../XMLSchema" i:type="d4p1:string"> at Microsoft.Crm.Extensibility.VersionedPluginProxyStepBase.Execute(PipelineExecutionContext context)
at Microsoft.Crm.Extensibility.PipelineInstrumentationHelper.Execute(Boolean instrumentationEnabled, String stopwatchName, ExecuteWithInstrumentation action)
at Microsoft.Crm.Extensibility.Pipeline.Execute(PipelineExecutionContext context)
at Microsoft.Crm.Extensibility.MessageProcessor.<>c__DisplayClass1.<RunStage>b__0()
at Microsoft.Crm.Extensibility.PipelineInstrumentationHelper.Execute(Boolean instrumentationEnabled, String stopwatchName, ExecuteWithInstrumentation action)
at Microsoft.Crm.Extensibility.MessageProcessor.RunStage(PipelineExecutionContext context, Int32 pipelineStage)
at Microsoft.Crm.Extensibility.MessageProcessor.Execute(PipelineExecutionContext context)
at Microsoft.Crm.Extensibility.InternalMessageDispatcher.Execute(PipelineExecutionContext context)
at Microsoft.Crm.Extensibility.ExternalMessageDispatcher.ExecuteInternal(IInProcessOrganizationServiceFactory serviceFactory, IPlatformMessageDispatcherFactory dispatcherFactory, String messageName, String requestName, Int32 primaryObjectTypeCode, Int32 secondaryObjectTypeCode, ParameterCollection fields, CorrelationToken correlationToken, CallerOriginToken originToken, UserAuth userAuth, Guid callerId, Guid transactionContextId, Int32 invocationSource, Nullable`1 requestId, Version endpointVersion)
at Microsoft.Crm.Extensibility.OrganizationSdkServiceInternal.ExecuteRequestRequestWithInstrumentation(OrganizationRequest request, CorrelationToken correlationToken, CallerOriginToken callerOriginToken, WebServiceType serviceType, UserAuth userAuth, Guid targetUserId, OrganizationContext context, Boolean returnResponse, Boolean checkAdminMode, Object operation)
at Microsoft.Crm.Extensibility.OrganizationSdkServiceInternal.ExecuteRequest(OrganizationRequest request, CorrelationToken correlationToken, CallerOriginToken callerOriginToken, WebServiceType serviceType, UserAuth userAuth, Guid targetUserId, OrganizationContext context, Boolean returnResponse, Boolean checkAdminMode)
at Microsoft.Crm.Extensibility.OrganizationSdkServiceInternal.ExecuteRequest(OrganizationRequest request, CorrelationToken correlationToken, CallerOriginToken callerOriginToken, WebServiceType serviceType, Boolean checkAdminMode)
at Microsoft.Crm.Extensibility.OrganizationSdkServiceInternal.Execute(OrganizationRequest request, CorrelationToken correlationToken, CallerOriginToken callerOriginToken, WebServiceType serviceType, Boolean checkAdminMode)</d2p1:value>
</KeyValuePairOfstringanyType>
<KeyValuePairOfstringanyType>
<d2p1:key>OperationStatus</d2p1:key>
<d2p1:value xmlns:d4p1="www.w3.org/.../XMLSchema" i:type="d4p1:string">0</d2p1:value>
</KeyValuePairOfstringanyType>
<KeyValuePairOfstringanyType>
<d2p1:key>SubErrorCode</d2p1:key>
<d2p1:value xmlns:d4p1="www.w3.org/.../XMLSchema" i:type="d4p1:string">-2146233088</d2p1:value>
</KeyValuePairOfstringanyType>
</ErrorDetails>
<Message>User with ID 6911f700-68b5-e711-80dd-00155da70437 does not have Update permissions for the erm_delegatetouser attribute in the erm_delegation entity. The erm_delegationid of the record is 7e3790f9-75bd-e711-80e8-00155da70437</Message>
<Timestamp>2017-10-30T13:26:48.98288Z</Timestamp>
<InnerFault i:nil="true" />
<TraceText>
[Microsoft.Crm.ObjectModel: Microsoft.Crm.ObjectModel.SyncWorkflowExecutionPlugin]
[9058d8b7-ed7c-e711-80d8-00155d366d3d: ]
Starting sync workflow 'Delegation - Set Delegate to (User) automatically', Id: 8758d8b7-ed7c-e711-80d8-00155d366d3d
Entering UpdateStep1_step:
Sync workflow 'Delegation - Set Delegate to (User) automatically' terminated with error 'User with ID 6911f700-68b5-e711-80dd-00155da70437 does not have Update permissions for the erm_delegatetouser attribute in the erm_delegation entity. The erm_delegationid of the record is 7e3790f9-75bd-e711-80e8-00155da70437'
</TraceText>
</OrganizationServiceFault>