I came in to work this chilly Monday morning to find out that the navigation on our Intranet is gone...
We're using managed navigation used accross all sites. No way I could recreate it as a structured navigation.
I went to check the Managed Metadata service immediately, only to confirm it's not accessible:
Many people posted about such an issue and some of them suggest it has occured after applying Windows or SharePoint updates. We, however don't apply any updates automatically and I haven't applied any updates recently either.
I verified all the permissions on the Managed Metadata Service and they all seemed intact.
App. pool recycle / iisreset did not help at all.
I tried to restore the Metadata database but that didn't help. I could just access the application, but then it was empty. In SQL, I could see that the terms are still there when I did a SELECT on the table (I know it's not the best idea).
I also tried this solution but it didn't work for me. Like switching back to the original database would not succeed, but it would never return an error either. I could access the application with this solution, but not see any of our terms.
Then I tried this solution of a MCM but that didn't work for me either...
Finally I've got to this and that worked. All data was there and our navigation has appeared immediately after an iisreset.
Detach the database
Deleted the Managed Metadata service application in CA
Create a new managed metadata service application (but I have used the same app. pool and the same account as before, contrary to the article)
Add the newly created service application to the farms default list
Switched to a different database name, for example Metadata_Test
Restored the original Metadata database from the last backup taken overnight.
Changed the properties of the service app, and switched to the name of the restored (original) DB.
And it's all good now.