So in my project plans the renumberoption is always greyed out. I inheritted this plan from others and the WBS codes were all over the place, (EG sequence: 22.214.171.124.3, 5.1, 126.96.36.199.2, 09-12). There was no custom code setup this had just been corrupted along the way somehow. To fix it I was going to follow the Outline Number workaround. However all I actually had to do was highlight each of the WBS tasks in the plan (note I did not select the column, click the first task – hold shift – click the last task – all withing the WBS column) and then press ‘Delete’. When I pressed ‘Delete’ the numbers there were removed and automatically replaced with the correct number format that MPP defaults to. Hope this helps others.