Hi Lovena,
Please follow below steps :-
1) check the communication channel is active or not ?
2) check the if the error is resolved by using cache refresh for not
http://host:port/CPACache/refresh?mode=full delta
3) if not, remove the communication channel and create again and activate (simple method is copy the cc to cc1, again delete cc, again copy cc1 to cc and activate).
Now resend the failed messages in ABAP stack
Regards
S Tomar