Are you trying to figure out why you can’t add notations to the AR invoice? Are all the icons disabled in the toolbar of the AR notation dialog box?
Chances are you have the PRINTED checkbox checked for the invoice (in the header area). You’ll need to uncheck this in order to add your notes to the invoice.
By the way, you don’t have to save the invoice with the printed unchecked. VISUAL will allow you to add your notes simply by unchecking it.
Go ahead and have a look at that invoice you can’t add notes to. Was the checkbox checked? Yes?