getting sqlcode -206

i m working on mainframes, coding in cobol and db2
EXEC SQL
UPDATE BOOKS_STAT17
SET STATUS1 = 'O' , EMP_NUMBER=NULL
WHERE COPY_NUMBER = WS-COPY-NUM
AND ISBN_NUMBER = WS-ISBN-NUM
END-EXEC.
error i m getting:
DBH3 BIND SQL ERROR
USING TRG4SUSR AUTHORITY
PLAN=MONIKA
DBRM=RETURNS
STATEMENT=142
SQLCODE=-206
SQLSTATE=42703
TOKENS=WS-ISBN-NUM
CSECT NAME=DSNXORSO
RDS CODE=-100

how 2 fix it?

re: getting sqlcode -206

This question is being moved to the DB2 forum.

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re: getting sqlcode -206

i know this is months later, i was looking for some answers and came accross this question. it appears they forgot the : in front of the host var.