ERROR [HY000] [Oracle][ODBC][Ora]ORA-01843: not a valid month

Question

SELECT /*+ INDEX(POLICY_WORK I_AR_DT) */
"TIPS"."POLICY_WORK"."AGENT_ID" AGENT_ID,
SUM(NVL("TIPS"."POLICY_WORK"."ADJ_RATED_EXPSRE_AMT", 0)) RATED_EXPSRE_AMT,
SUM(NVL("TIPS"."POLICY_WORK"."ADJ_PREM_AMT",0)) FUND_PREM,
SUM(NVL(DECODE("TIPS"."POLICY_WORK"."PRMLGTD_AMT","TIPS"."POLICY_WORK"."ADJ_PRMLGTD_AMT",1,0),0)) COUNT
FROM "TIPS"."POLICY_WORK"
WHERE "TIPS"."POLICY_WORK"."AGENT_ID" = :a_agent_id
AND TO_DATE(TO_CHAR( "TIPS"."POLICY_WORK"."AR_DT",'MM/DD/YYYY') ,'MM/DD/YYYY')
BETWEEN TO_DATE('01/01/'||TO_CHAR(TO_DATE(:a_start_date,'MM/DD/YYYY'),'YYYY'),'MM/DD/YYYY')
AND TO_DATE('01/01/'||TO_CHAR(TO_DATE(:a_end_date,'MM/DD/YYYY'),'YYYY'),'MM/DD/YYYY')
AND ( "TIPS"."POLICY_WORK"."TRAN_ID" > 999 )
GROUP BY "TIPS"."POLICY_WORK"."AGENT_ID";

"TIPS"."POLICY_WORK"."AGENT_ID" = 4555001, this is the value I am entering in my query I am getting positive result only but if I enter the same value into the parameter then it is not working

In this query i'm adding a_agent_id parameter, after try to run the query in powerbi report builder the error showing invalid month, in this query  what is the error