@RameshN3   this issue appears to be a PostGres issue, rather than Pega.  Did you check with the DB vendor?

Perhaps you could check the following:

https://stackoverflow.com/questions/43211296/pgadmin4-postgresql-application-server-could-not-be-contacted

Other suggestions:

https://postgresrocks.enterprisedb.com/t5/EDB-Postgres/pgAdmin-v4-The-application-server-could-not-be-contacted/td-p/2006/

https://www.pgadmin.org/docs/pgadmin4/development/connect_error.html

If pgAdmin displays this message, there are two possible reasons for this: the database server isn't running - simply start it. the server isn't configured to accept TCP/IP requests on the address shown.

In case it is  attempting to use the sessions from the prior version:

 If running the pgadmin 4 by Administrator is not helpful in your case then try clearing out the "C:\Users\{YourUser}\AppData\Roaming\pgAdmin" folder. 

Alternatively, to resolve PgAdmin Fatal Error:

https://postgrespro.ru/list/thread-id/2507859

• Take the backup of the 'pgadmin4.db' file located at "C:\Users\<user_name>\.pgadmin" and then delete it.
• Restart the pgAdmin4.

It would be best if you check with the DB vendor and network team.