How to call function locate in window.opener

Hi, In Parent window, i try to pop-up a child window, in the child window got a Iframe. Iframe will do some process and afterthat it will call a function in Parent window. I get the error message - "Object doesn't support this property or method"
I use the following syntaks :
window.opener.passvalue(Id);

//passvalue locate function in Parent window

Thanks.