Oracle forms 6i problem

To update rows in a Table ,i gave Table name dynamically but it is not woking in forms 6i.
ex:
Lvstring:=UPDATE testsum t SET t.pr_sm_cfch=(SELECT t.pr_sm_cfch+b.pr_sm_cfch FROM ' ||' '|| [B]Tablename[/B] ||' '|| ' b WHERE t.pr_sm_tokn=b.pr_sm_tokn AND (T.PR_SM_PERD,T.PR_SM_TOKN) IN
(SELECT MAX(PR_SM_PERD),PR_SM_TOKN FROM pr_wsum_yr
GROUP BY PR_SM_TOKN) AND t.pr_sm_mode='||''''||'W'||''' AND b.pr_sm_mode='||''''||'W'||''')
WHERE t.pr_sm_mode='||''''||'W'||''' AND (T.PR_SM_PERD,T.PR_SM_TOKN) IN
(SELECT MAX(y.PR_SM_PERD),y.PR_SM_TOKN FROM pr_wsum_yr y
WHERE y.PR_SM_MODE='||''''||'W'||''' GROUP BY y.PR_SM_TOKN)
AND t.pr_sm_tokn IN (SELECT pr_sm_tokn FROM'||' '|| t ||' '|| 'WHERE
pr_sm_mode='||''''||'W'||'''' ;
forms_ddl(Lvstring) is not working for Update . What command i need to use
pls suggest me.