In some cases you can modify the wsdl that Mendix will accept the webservice and communicate succesfully. Store the wsdl on disc and remove the mixed content. Can you post (a part of the) wsdl?
EDIT: Remove the mixed=true and replace the 'any' with typed ones
extract from wsdl
<s:complextype> <s:sequence> <s:element name="AllResult" >="" <s:complextype="" mixed="true"> <s:choice minoccurs="0" maxoccurs="unbounded"> <s:any processcontents="lax"/> </s:choice> </s:complextype> </s:element> </s:sequence> </s:complextype> </s:element> <s:element name="Cash"> <s:complextype> <s:sequence> <s:element name="Fund" type="s:string" minoccurs="0"/> </s:sequence> </s:complextype> </s:element> <s:element name="CashResponse"> <s:complextype> <s:sequence> <s:element name="CashResult" >="" <s:complextype="" mixed="true"> <s:choice minoccurs="0" maxoccurs="unbounded"> <s:any processcontents="lax"/> </s:choice> </s:complextype> </s:element> </s:sequence> </s:complextype>