Hi,
Your web service is most likely using ISO-8859-1 encoding, which is not supported in the WCF-BasicHttp adapter in BizTalk. Try using the WCF-Custom adapter as the Transport Type, and in the Binding tab in the Transport Properties window, select customBinding as the Binding Type, then, under the Binding panel, click on the textMessageEncoding extension to bring up its properties (in the Configuration panel), and enter ISO-8859-1as the value for the field writeEncoding.
Hopefully, this should solve your issue.
Daniel.