Here is my SOQL:

SELECT Id,Cross_Section__r.Name,(SELECT Id FROM Cross_Section__r) FROM SAS_Product_Type__c

Here is the error:

Cross_Section__r.Name,(SELECT Id FROM Cross_Section__r) FROM SAS_Product_Type__c
                                      ^
ERROR at Row:1:Column:49
duplicate field selected: Cross_Section__r

Looks like the Child Relationship Name of Cross_Section__r and its parent object of SAS_Product_Type__c and the Lookup field of Cross_Section__c on SAS_Product_Type__c are being flagged as duplicates.

The Cross_Section__r child records is where we record each section of a cross section on the SAS_Product_Type__c with lengths and angles, whereas the Cross_Section__c lookup is to the File object for attaching an image of the cross section.

I found a post about without and answer. So I answered it. 😃

DeveloperForce