Hi Satish,
You cannot activate the activated object in repository, this object has been activated in repository, so if you do not want to see this error or delete this error, you can operate based on below process.
open window menu ->show view->others->General-> choose problems, you can right-click corresponding error information to delete this error records, after that it will display correctly.
For Q2, you need to add single quotes, please try below script.
CALL "_SYS_REPO"."GRANT_SCHEMA_PRIVILEGE_ON_ACTIVATED_CONTENT"('SELECT','"sridhar1"','SYSTEM');
Regards,
Jerry