Edit a SharePoint task list in Microsoft Project Professional 2013
When a SharePoint task list is visible in Project Web App, but not editable, it is still possible to edit a task list in Microsoft Project Professional 2013. If you want to edit a task list in Project Professional 2013, there are two options:
When you make changes to a task list by using Project Professional 2013, those changes are saved to an MPP file on the site that contains the task list. If you decide to use Project Web App to edit your task list, and follow the steps in Change a SharePoint task list into an enterprise project, you also have to follow additional steps to ensure that the edits you’ve made within the MPP file are appropriately transferred to Project Web App.