If you realized content database still remain at the Manage Content Databases section in Central Administration. When try to delete this database you received “Object reference not set to an instance of an object.” or by using stsadm getting belowed errors.
C:\>stsadm -o removecontentdb -url http://blog.bugrapostaci.com -databasename ”Sharepoint_blog_db” -databaseserver DBBLOG
Database “Sharepoint_blog_db” is not associated with this web application
C:\>stsadm -o addcontentdb -url http://blog.bugrapostaci.com -databasename ”Sharepoint_blog_db” -databaseserver DBBLOG
An update conflict has occurred, and you must re-try this action. The object SPWebApplication Name=blog.bugrapostaci.com Parent=SPWebService is being updated by POSTMAN\bugra, in the w3wp process, on machine BLOGSERVER. View the tracing log for more information about the conflict.
This issue occurs if the contents of the file system cache on the front-end servers are newer than the contents of the configuration database. After you perform a system recovery, you may have to manually clear the file system cache on the local server.
Clear the file system cache on all servers
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