webservice oneway and new SPSite(myUrl)

Hi,
i have a problem with a oneway web methodthat open a moss site (probably because in a oneway webmethod the context is null)

Is possible to rewrite this code to remove the null reference exception? (without the oneway attribute i  don't have the exception)

[SoapDocumentMethod(OneWay = true)]
        [WebMethod(Description = "TestOneWay")]
        public voidTestOneWay(string webUrl)
        {
using (SPSite site = new SPSite(webUrl))
            {
....
}
}

the exception is:

[2304] Error:Object reference not set to an instance of an object.
[2304] w3wp.exe Error: 0 :
[2304StackTrace:   at System.Web.Hosting.ISAPIWorkerRequestInProc.GetAdditionalServerVar(Int32 index)
[2304]    at System.Web.Hosting.ISAPIWorkerRequestInProc.GetServerVariable(String name)
[2304]    at System.Web.HttpRequest.AddServerVariableToCollection(String name)
[2304]    at System.Web.HttpRequest.FillInServerVariablesCollection()
[2304]    at System.Web.HttpServerVarsCollection.Populate()
[2304]    at System.Web.HttpServerVarsCollection.Get(String name)
[2304]    at System.Collections.Specialized.NameValueCollection.get_Item(String name)
[2304]    at Microsoft.SharePoint.SPGlobal.CreateSPRequestAndSetIdentity(Boolean bNotGlobalAdminCode, String strUrl, Boolean bNotAddToContext, Byte[] UserToken, String userName, Boolean bIgnoreTokenTimeout, Boolean bAsAnonymous)
[2304]    at Microsoft.SharePoint.SPRequestManager.GetContextRequest(SPRequestAuthenticationMode authenticationMode)
[2304]    at Microsoft.SharePoint.Administration.SPFarm.get_RequestNoAuth()
[2304]    at Microsoft.SharePoint.SPSite.CopyUserToken(SPUserToken userToken)
[2304]    at Microsoft.SharePoint.SPSite.SPSiteConstructor(SPFarm farm, Guid applicationId, Guid contentDatabaseId, Guid siteId, SPUrlZone zone, Uri requestUri, String serverRelativeUrl, Boolean hostHeaderIsSiteName, Uri redirectUri, Pairing pairing, SPUserToken userToken)
[2304]    at Microsoft.SharePoint.SPSite..ctor(SPFarm farm, Uri requestUri, Boolean contextSite, SPUserToken userToken)
[2304]    at Microsoft.SharePoint.SPSite..ctor(String requestUrl)
[2304]    at Reply.Moss2EAI.SPHandler.GetAllFlowConfiguration(String webUrl, String flowConList)
[2304]    at Reply.Moss2EAI.EaiMossIntegration.GetMessagesFromEai(String webUrl, String listName, String applicationName)