Commander this state cannot be stacked, if this items is used, the previous state will be replaced..

The message is the game warning you that activating a buff, such as a peace shield or a bonus score ticket will replace any existing buff of that kind. For example activating a 50% extra score ticket, when one is already active does not give you 100% extra. The new ticket will simply cancel the old ticket.

There is a bug in the game though that means it will show this message even if there is no existing ticket active (for 50% Clash of zones score tickets anyway). If you have no existing running ticket the don't worry about it.