Please note when RAC you need to define scope=both

IE:

**Check if there are any hidden "_" parameters.**

    SQL> SELECT name,description from SYS.V$PARAMETER WHERE name LIKE '\_%' ESCAPE '\';


**Remove the hidden parameter, In my case it is "_rac_dbtype_reset"**

    SQL> alter system reset "_rac_dbtype_reset" scope=both;

**Check again**

    SQL> SELECT name,description from SYS.V$PARAMETER WHERE name LIKE '\_%' ESCAPE '\';



**Then STOP and START the DB on ALL NODE in the RAC**

    SQL> shutdown immediate;

    SQL> startup;