Location > Custom". I am finding that when I open a ditamap using this extended framework (and yes, the correct associations have been made in the "Association rules"), I cannot seem to get the "Open Maps in editor with resolved topic"

Hi, I am developing a framework which is extending the existing DITA framework. The new framework is distributed via our source control and so it needs to be pointed to via the "Preferences > Document Type Association option working. I have checked that the file is not locked and that I am able to do other operations (like create reusable content etc). What am I doing wrong? Any help would be greatly appreciated. Thanks, Nathan