As above, if one is in an area of the cabin with the allocation full (for the particular status level) then you won't be able to select anything further, while someone of a higher status may be able to.
For example no status flyers are often restricted from forward rows when booking.
This can often change at T-80 when, in theory, the allocations open up more and a more forward seat can be chosen.
providing the specific date may help to confirm this is the situation as many of us can check how the map looks.