Hi AakanKsha,
The External Control has only sense when you want to start/stop/active/inactive your channel outside or inside of the CCM but afaik it has not relation with the possibility of any issue when the channel deals with an inbound or outbound message and obviously the channel is green in running mode.
On the poll channels you can have any problem with backgrounds process that it uses, but i think this is not your case.
Could you share the exception that you are getting?
Regards.