unable to rebuild indexes

I have upload data usinh sqlldr direct=TRUE parallel=TRUE skip_index_maintenance=true. now index is unusable.

I need to rebuild index.

SQL> alter index HUA_INDEX1 rebuild online parallel 6;
alter index HUA_INDEX1 rebuild online parallel 6
*
ERROR at line 1:
ORA-12801: error signaled in parallel query server P003
ORA-01722: invalid number

SQL> alter index HUA_INDEX1 rebuild online;
        alter index HUA_INDEX1 rebuild online
                 *
ERROR at line 1:
ORA-01722: invalid number

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CREATE TABLE "UDARA"."HUA"
  (
    "A_NUMBER" NUMBER(10,0) NOT NULL ENABLE,
    "B_NUMBER" CHAR(10 BYTE) NOT NULL ENABLE,
    "INS_DATE" DATE NOT NULL ENABLE,
    "TIME"     NUMBER(6,0) NOT NULL ENABLE,
    "C_NUMBER" VARCHAR2(40 BYTE) NOT NULL ENABLE