Hi might be able to answer this
I have had the same problem and mostly it comes to the fact that my Corona Licserver-laptop has installed updates
and has rebooted >> LicServer is not running and the nodes which try to connect to the server wont get licenses and 3dsmax says error (in backburner).
I had this problem just last week again. Have to put that licserver-program to start with Windows (8).
EDIT: Would be cool if the Corona Warning window in 3dsmax could sniff that the DrNodes cant connect to the licserver!
Making sure that it is possible for Corona to access the folder with the license (e.g. there may be a problem if %localappdata% folder is moved to some other place)
Re-installing 3ds Max, Backburner, and Corona (this might not sound good, but it actually helped in one case)