If it is any help,I had the same problem.My solution was to take the view that no POS machine was going to defeat me when I pay for its electricity,peripherals,connection and everything else.So...
I pressed the red X,and nothing happened.I refreshed the page,and did it again.this time it worked and I was able to leave a message for the member I was offering the door to.
I found that I then had to refresh several times in order for the action to take effect,and then gave up to wishing things would work as they ought and carried on flushing deadwood in the same manner,for three nights on the bounce,using this same method.
Once the system had me figured for the boss,it stopped resisting(like most people,it realised resistance was futile against me)
I do this also with messages to friends in "My messages" because the first,second and third attempts to get my message to send(using the "Send" button) always fail.The fourth one works just fine,and I am rewarded for my tenacity with my message resplendant on my recepients page.
You can,if you wish,call me cynical,however,my friends call me
Lizzie