To all those people that are still having trouble and have tried everything in the forum with no luck
I HAVE A FIX FOR YOU TO TRY (TESTED 3 TIMES)
iDisplay screen mirroring app was the fault for me
I installed it but delete it straight away by removing it from application to recycle bin wrong move number 1
I have also uninstalled it using CleanMyMac with no luck ( wrong move there number 2)
all with restarts but it doesn't remove all files folders & drivers
what needs to be done is use the uninstaller in the program
download it again if necessary from www.getidisplay.com
you DO NOT have to install it again
just run the iDisplay.DMG file you downloaded from the website above
click uninstall
which will give you an error saying file is corrupt
if this is the case
this is what you need to do
first which is REALLY IMPORTANT go to the location below first and change a setting or it wont work :-)
system preferences
security & privacy
and change the setting at the bottom to ALLOW APPS FROM ANYWHERE
doing this will allow total removal
then run the iDisplay installer again which has the built in uninstaller you ran before
click uninstaller and follow the prompts to remove it totally
l have now uninstalled iDisplay without an error saying the uninstaller is corrupt
followed by a restart
now everything is working great again
THATS IT, ALL DONE!!!!! enjoy your streaming