A colleagua of mine ran into a problem when he wanted to clone a database
that didn't exist anymore.
Solution in Oracle 11G (Of course you must have a backup of that database)
In rman do not connect to the target database (it isn't there anymore)
connect catalog rmnt_own/@OCRM51P
connect auxiliary /;
set dbid=3870197482 # That is something you have to know because that is the id of the database
you want to clone
duplicate database AVC452T TO AVC452C
until time "to_date('2012-04-02 00:30:00','YYYY-MM-DD HH24:MI:SS')" ;
And that is it.