Web service call - underlying connection closed

We have an ASP.NET web service, Framework 2.0 running under IIS 7 + Windows 2008. After working fine in Integration and QC the service has moved to production and any call开发者_开发技巧s to the service bomb out. We added a test method that returns a string- this works but the others that take complex types don't. Here is the stack trace:

The underlying connection was closed: An unexpected error occurred on a receive. System.Web.Services at System.Web.Services.Protocols.WebClientProtocol.GetWebResponse(WebRequest request) at System.Web.Services.Protocols.HttpWebClientProtocol.GetWebResponse(WebRequest request) at System.Web.Services.Protocols.SoapHttpClientProtocol.Invoke(String methodName, Object[] parameters) at

httpett.log says: Connection_Abandoned_By_ReqQueue

We've tried switching to classic mode, re-registering ASP.NET and are now considering rolling it out in prod on W2003.

Any ideas anyone?