EXTENSION X is not supported by Form Editor

Hi,

We would like to see the project XML to investigate the extension error, you can send us the project on support ticket. I can refer this to the developers so they can investigate further. To send the Project XML, Right click on the project > Export project.
http://www.soapui.org/Support/support-overview.html

For now I would suggest you to try XML request editor to populate your requests. Default your view to XML editor (Click on File > Preferences > SoapUI Pro tab > Set Default Request editor to Source). Do not switch between XML and Form view. I believe you should be able to setup your SoapUI Pro test cases from XML view. You can use property expansion in XML view.

Since you are new to SoapUI Pro, you can refer this link for functional testing,
http://www.soapui.org/Functional-Testing/functional-testing.html

To attach attachments,
http://www.soapui.org/SOAP-and-WSDL/adding-headers-and-attachments.html

Thanks,
Jeshtha