Within the P6 resource usage view there is a function at the bottom left corner of the screen, the following is from P6 help:

Filter activities according to the Resource Usage Profile

When viewing the Resource Usage Profile for a specific project, you can filter the activities displayed in the Activity Table, Gantt Chart, Activity Usage Spreadsheet, or Activity Network, so that they correspond to the resource information currently displayed in the profile.

To display only the activities to which a specific resource has been assigned, in the left pane of the bottom layout select the resource, then, in the Display Activities for Selected section, mark the Resource checkbox.

To display only the activities to which a specific resource has been assigned within an individual timeperiod, in the left pane of the bottom layout select the resource, then, in the Display Activities for Selected section, mark the Time Period checkbox. In the Resource Usage Profile, click the timeperiod for which you want to display the resource's activity assignments.

Note

When you mark the Time Period checkbox, the currently selected timeperiod highlights and the cursor changes to a crosshair when you position it within the Resource Usage profile. When you select a timeperiod, it is highlighted and the activities in the Activity Table, Gantt Chart, or Activity Network are filtered to correspond to the timeperiod.

The problem I have is that this function is disabled (greyed out), does anyyone know how to enable this function as I can not find anything within setting, preferences etc

Thanks