Oracle Procedure errors

Hi All,

I am new to Oracle Procedure,Please help me to  solve the following errors...i am to run SQL query  Successfully!!!..But i am executing the procedure

ORA-01722: invalid number

ORA-06512: at "CREATE_NEXT_YEAR_PERIODS", line 5

ORA-06512: at line 1

CREATE TABLE ACPERIOD(  COMPANY_ID            VARCHAR2(2 BYTE),  PERIOD_ID             VARCHAR2(6 BYTE),  PERIOD_DES            VARCHAR2(100 BYTE),  PERIOD_BEG            DATE,  PERIOD_END            DATE,  CLOSED                VARCHAR2(1 BYTE),  YEAR_END              VARCHAR2(1 BYTE),  FA_PROCESS            VARCHAR2(1 BYTE),  AC_YEAR               VARCHAR2(4 BYTE),  RECONCILED            VARCHAR2(1 BYTE),  OH_PROCESS            VARCHAR2(1 BYTE),  QUARTER_ID            VARCHAR2(2 BYTE),  AC_YEAR_REPORT        VARCHAR2(4 BYTE),  JOB_VALUATION_POSTED  VARCHAR2(1 BYTE),  A_PERIOD_DES          VARCHAR2(100 BYTE),  VAT_RETURN_VALID      VARCHAR2(1 BYTE));------------------------------------Procedure--Create or Replace Procedure Create_Next_Year_periods(I_Companyid varchar2,I_Ac_Year varchar2 ) asbegin  FOR a IN 1..12 LOOP  Insert into AcPeriod(Company_id,PERIOD_ID, PERIOD_DES,  PERIOD_BEG, PERIOD_END,   CLOSED, YEAR_END, FA_PROCESS, AC_YEAR, OH_PROCESS, RECONCILED, QUARTER_ID,JOB_VALUATION_POSTED,A_PERIOD_DES,VAT_RETURN_VALID)  select Company_id,Period_id,To_Char(Period_beg,'MON-YYYY') PERIOD_DES,Period_beg,Period_End,closed,year_end,FA_PROCESS,Ac_Year,OH_PROCESS,RECONCILED,QUARTER_ID,JOB_VALUATION_POSTED,A_PERIOD_DES,VAT_RETURN_VALID from(    (Select I_Companyid Company_id, I_Ac_Year||LPAD( a, 2,'0') Period_id,   TO_CHAR(TO_DATE(I_Ac_Year||LPAD( a, 2,'0'),'YYYYMM'),'DD/MM/YYYY') Period_beg, TO_CHAR(LAST_DAY(TO_DATE(I_Ac_Year||LPAD( a, 2,'0'),'YYYYMM')),'DD/MM/YYYY') Period_End,  'N' CLOSED, decode(LPAD( a,