CryptoLib.decryptClobData DECRYPT CLOB

I am trying to decrypt a CLOB but keep getting an errors...We are using Oracle 11gR2.  Basically getting the ORA-06512 msg when I call this function:  Can anyone point me in the correct direction?  FYI, if the CLOB is less than 4000 then it works, but if it larger than 4000 then it gives me the above error.  I know 4000 is the max length for a VARCHAR2 but I am not passing a VARCHAR2 so dont understand where that is coming from.      
FUNCTION idecryptCLOB (
      p_clob   CLOB,
      p_key     VARCHAR2,
      p_type      NUMBER
   )
      RETURN CLOB DETERMINISTIC
   AS
      LANGUAGE JAVA
      NAME 'CryptoLib.decryptClobData(oracle.sql.CLOB, java.lang.String, int) return oracle.sql.CLOB';