As this message clearly explains, this
error means that the operation you are going to perform that returned this
error, needs database to be mounted EXCLUSIVELY - by only one instance. In my case, I was trying to drop a RAC database when I
faced ORA-01586. I realized that the other instance of my RAC database is still
up and it is needed that all the instances of a RAC database should be down
before we can drop a database.