RMAN-01009: syntax error: found "clone": expecting one of: "double-quoted-string, identifier, single-quoted-string"

Some of you might get into following problem. You want to duplicate a database and your duplicate command is the following:

RMAN> duplicate target database to dbsoandso nofilename check;

But RMAN returns following error: 

The solution is easily readable from the RMAN answer, but the one or the other person might not understand the problem immediately. So the mistake you have done is that you have forgotten the commas in:

RMAN> duplicate target database to dbsoandso nofilename check;

and it should be :

RMAN> duplicate target database to 'dbsoandso' nofilename check;