Hi Bet thanks for your inputs and sorry for replying late.
yes the blogname did conatined a valid name.After days of searching i found that the issue was the encoding which was mentioned in wp-config file.
originaly it was set to define(‘DB_CHARSET’, ‘utf8mb4’);
Due to this WordPress was not able to create necessary multisite tables for given subsite eventhough it created subsite on UI front.Changed that to utf8 encoding like define(‘DB_CHARSET’, ‘utf8’) and it worked like a charm.