No, you cannot use both authorize,net and paypal at the same time.
The problem is occurring with shipping rate lookup, what shipping provider are you using?
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.