Hello!
I've tried recreating this, but it seems to work just fine when I try it on my machine. The problem is occurring in XmlBeans, which is a third party library that soapUI uses to interact with XML. XmlBeans is not allowing your schema to compile. According to the specification, xsd:all can be used in an extension, given that the base model has an empty content model. Can you try removing the empty xsd:sequence from the base model? I think this might be causing the problem.
Also, which version of soapUI are you using? It may be that this is an issue with an older version of XmlBeans, used in an older version of soapUI.
If this doesn't help you with your issue, could you possible attach your entire WSDL so that we may further troubleshoot?
Regards,
Dain
eviware support