@Anonymous User
Have a quick read about this guide article about managing your devices.
http://help.nowtv.com/article/Managing-Devices
It sounds like that you have reached your four device limit on your account and i would suggest jumping over to nowtv live chat by clicking on the link page below to see if they will free up a slot for you.
http://help.nowtv.com/contact-us/Managing-Devices
If you don't watch nowtv on your mobile casting device, then to avoid the Chromecast counting has a second device, then if you cast the nowtv app to your Chromecast before playing anything this will then only count has one device.
Should you play the nowtv stream initially on your mobile casting device then cast to the Chromecast this will count as two devices against your nowtv account.
Or does the message says that you have reached the two simultaneous streams on your account ?
