[JS][CS5] Identifying a page item by its ID number

Hi All.

I have seen other posts that list an answer to this, and I am using syntax as per the post, but when I use this:

            myFrame = myPage.pageItems.ItemByID(myTextFrameArray[n]);

I get the error:

ReferenceError: myPage.pageItems.ItemByID is not a function

myPage is a valid page.

myTrextFrameArray does contain ID numbers of the text frames i need to process.

Any help with this would be great!

Cheers

Roy