I tried to send a book recently and wanted to use delivery confimation and I got a message saying that DC could not be used fot that address?! Why is that? I don't think there was anything wrong with the address cause I went and printed shipping through paypal so that I could have some type of delivery confimation and it went through just fine there

PayPal will convert the address you submit to them to the PO correct address, whereas PBS takes the addy just as the requestor puts it in.

You could have taken the addy, gone to the PO site, to their PLUS+4 page, standardized the addy, then used the custon DC page, input the changed addy and done it that way, but standardly the PBS address is exactly as the requestor inserts it.

ETA: DC can only be used on an address that is standardized to meet the USPS regs.