We have come across a strange issue this afternoon that the SharePoint root site collection went Read-Only and none of the users were able to perform any kind of admin operations.
Per our research, we could understand that the SharePoint site collection might have gone Read-Only because of a scheduled STSADM back-up running at that point of time.
With the release of SP2, the “SetSiteLock” option is now ON be default which means that the Site collection is read-only during the back-up operation.
To determine the lock status of the site, you can use the following getsitelock syntax:
stsadm -o getsitelock -url http://server_name
After the site has been backed up, you can use the none parameter of the setsitelock operation to remove all locks to the site:
stsadm -o setsitelock -url http://server_name -lock none
For more information, please refer these articles: