iMessage not working on MacBook pro

all of a sudden this morning iMessage is not working on my MacBook Pro. All text messages are still there but now when i open one the persons name is in red. when i click on the arrow it tells me that number is not registered with iMessage. Persons name is there but in red now.

any and all help would be appreciated. It's working fine on my iPhone and iPad, just not the laptop.

thanks