I've used Yootheme Pro page builder ( [url removed, login to view]) for Joomla to build a site for a client. I initially built the site on a Linux server and built some Yootheme Pro Custom Elements and all was working fine. ( instructions half way down the page for custom elements with the title: Adding a custom Builder Element, [url removed, login to view]).
The client needs the site hosted on their IIS server. so I moved the site to their Windows IIS server and now the Custom Elements are not showing.
I've taken a fresh install of Joomla and a fresh install of Yootheme Pro and tested with a simple custom element and it doesn't work on my local windows machine using WAMP. I did the same thing on my MAC and it works fine.
I will need full information of the problem and how to fix.
You will be able to replicate the problem with a fresh install of Joomla and I will send you Yootheme Pro and a test custom element.
Full demonstration of the problem will be given over Skype and screen sharing.
This should be a quick debug for someone who knows what they are doing.