The Introscope Enterprise Manager cannot found Diagnostic Agent - SAP Solution Manager 7.2

I have installed Diagnostic Agent and connect to SAP Solution Manager 7.2 and Trusts this Diagnostic Agent. by the way the Introscope EM already install and running. After that I have change the password for user 'Admin' and 'Guest' of The Introscope EM. When I return to Discover Introscope EM - Mandatory Configuration - Step 4. Define CA Introscope, the issue happens with the error as the picture below that the Diagnostic Agent was not found, The Diagnostic Agent still running and being trust before and after re-install the Introscope EM.

For more information, I have installed Introscope EM with user Diagnostic Agent OS user and giving it permission to Read and Write to path /use/sap/ccms/apmintroscope.

Could everyone have any solution for this issue?
By the way, I want to know How Introscope finding the Diagnostic Agent?

Thanks.