What is on the first line of add_inv_create_items.php?
Is there a blank line or empty space between the includes?
The error implies there is a blank line or space on line 1 of that file.
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.