Now it seems obvious looking the exception generated. Thanks for the explanation.
You were right, the problem was the 's:Xml' type.
I have this definitions:
<definitions xmlns="
http://schemas.xmlsoap.org/wsdl/" xmlns:http="
http://schemas.xmlsoap.org/wsdl/http/" xmlns:mime="
http://schemas.xmlsoap.org/wsdl/mime/" xmlns:s="
http://www.w3.org/2001/XMLSchema" xmlns:s0="
http://www.sap.com/xMII" xmlns:soap="
http://schemas.xmlsoap.org/wsdl/soap/" xmlns:soapenc="
http://schemas.xmlsoap.org/soap/encoding/" targetNamespace="
http://www.sap.com/xMII">And this complexType:
<s:complexType name="InputParams">
<s:sequence id="InputSequence">
<s:element maxOccurs="1" minOccurs="0" name="REQUEST" type="s:Xml"/></s:sequence>
</s:complexType>
Changing from 's:Xml' to 's:string' made it work in SoapUI.
Actually, the WSDL with 's:Xml' passed in validation in eclipse, but I don't think it should. A long time ago, I used wsdl.exe (.NET) to generate C# code from WSDL, and I got a warning about this 'unknown' type - I just ignored it (and forgot!), as the code worked well (using a string instead of this type).