The cause is that the SAP Solution Manager is not configured properly.
In order for the SAP Solution Manager to be able to connect to the Automation Engine, you need to add the following lines both in Secinfo and Reginfo File tabs of the ACL Files which can be accessed from the transaction SMGW then click on Go to >> Expert Functions >> External Security >> Maintain ACL Files .
P TP=* HOST=<Hostname> ACCESS=* CANCEL=*
P TP=* HOST=local CANCEL=local ACCESS=local
P TP=* HOST=internal CANCEL=internal ACCESS=internal