Getting 'B-Tree structure is invalid' error

I received an error while trying to access a view. The error is "B-Tree structure is invalid." What exactly does this mean?
You either have a corrupt view or corrupt documents in your database. In either case, you should run the standard utilities of compact --B, fixup, and updall --R against the database to see if it fixes the error. If it doesn't work, you will need to try and restore the database from a backup.

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