SharePoint object [SPContentDatabase Name=""_Content] is in an unsupported state, and could not be used by the current farm.
From the error message, it seems that the SPContentDatabase Name=""_Content is in an unsupported state.
Have you installed any update recently?
Check the Database status, whether it is need upgrade.
You can create a new content database for the web application, and create site collection in the new content database.
I think you may have to re-run the configuration wizard for this issue. The root cause of this we will get to know if we go the upgrade status page from the central admin, we will see that last patch update status was not succeded it will be shown as Failed, so when the patch update was done it was not checked properly. The patch update status we can see as below:
If we check the ULS log, we will get the log something like below:
Looking at the logs, there are but two errors listed:
“Database [CONTENTDB] contains a site (Id = [GUID], Url = [SITEURL]) that is not found in the site map. Consider detach and reattach the database.”
“Database [CONTENTDB] contains a site (Id = [GUID], Url = [SITEURL]) whose url is already used by a different site, in database (Id = [GUID], name = [CONTENTDB2]), in the same web application. Consider deleting one of the sites which have conflicting urls.”
The reason for patch update failure could be many reasons, but the above scenario is one of them, so you can check your ULS log and troubleshoot accordingly. For this particular ULS log, we can fix the issue by cleaning up the orphan site - however, if this is in the production server it will be risky to clean up the orphan site without proper planning. So it would be best to re-run the configuration wizard but you must take all necessary backup before going for the re-running the configuration wizard and follow the MSDN guidelines for running the configuration wizard and finally make sure your server upgrade status shows as "Succeeded"