The schedule in Primavera P6 was all alright, everything worked great with all previously entered activity codes working exactly as they are supposed to. Sorted the schedule using them, and created a specific layout for this project which made life a lot easier. But suddenly no longer have any activity codes or wbs codes appearing on the screen.
This kind of problems happens in Primavera P6 when you open project and there was a an active filter before you close Primavera. In Group & Sort, you have to uncheck the tick box to make sure that all your WBS or Activity codes will still appear on the screen even they are empty. Sometimes in Primavera P6 WBS and Activity codes become empty because the activities in them become hidden due to an active filter.
Check also your User Preferences settings, (Edit\User Preferences\Startup Filters)? Change the startup filter for activity codes to “View All Data (No Filter)”, then try to login in again and check your Activity code details.