When checking the tomcat/logs/server.log, we saw the error:
[sm] kmsecurity not found in user context for user
It seems that we have missed the KM configure in SM, so the next action we need to complete is: go to Knowledgebase Management > Administration > Environment> SRC? => checked, choose the KM Server, then click Save > click Full Reindex
Wait for 5 mins and it will finish the index
Now, open up the SRC page again. You should get the login page normally.