What triggers "Can't Revenge"

[James-6655]

Ocassionally i will see "CAN'T REVENGE" after the names of someone who has attacked me in PVP and I'm not able to attack back. Anyone know what triggers this?

[Bengio]

You can only use revenge twice

[Bengio]

Against the same player
And 20 per day

[James-6655]

Thanks. Now I know why I get so many on Saturdays.