Thanks for your reply.
Yes, Installed new moodle is working fine now also.
FYI - I had done migration steps as below,
1) Created a new database for migrated moodle and imported old/working moodle DB backup.
2) copied all moodle contents to a new folder i.e, migmoodle.
3) next, copied all moodledata contents to a new folder i.e, migmoodledata.
4) finally, I had made required changes in config.php with the migrated moodle names and DB details.
5) At last, accessed the moodle and got the same error "Error reading from database".
Just now also, I had tried same steps again and successfully got the same error
Kindly look into my steps and let me know if I made any mistakes in the migration process.