Reply To: Invoice error

The invoice error will be hard to find. All I can say is that before my scripts get executed there’s already something in the output. Probably there’s a whitespace in one of the loaded files.
On this two pages you can find more informations on how to find them:
http://kb2.adobe.com/community/publishing/505/cpsid_50572.html
http://codex.wordpress.org/FAQ_Troubleshooting

For the datepicker the problem is a bit more clear. Your theme is including jquery and datepicker on its own, but it does it wrong and doesn’t check if it’s already loaded and replaces it. Cause of that there are two versions loaded of both and they conflict each other. I would ask the theme developer to fix it. Here’s how to do it right:
http://wp.tutsplus.com/articles/how-to-include-javascript-and-css-in-your-wordpress-themes-and-plugins/

Regards