Throwing an exception when trying to attach a document to a list item

[JimmyRopes]

I am throwing a System.ArgumentException () when trying to attach a document to a list item.

This is the code I am using. I had log statements in (since removed to cut down on extraneous code) that show me that I am getting up to the <pre>Item.Attachments.AddNow(FileName, binFile);</pre> statement when the exception is being thrown.

FileName is a String passed as a parameter to the web service.

Can anyone spot what I am doing wrong?

<pre lang="c#">
// open prototype site and web
site = new SPSite(SPContext.Current.Web.Url);
web = site.OpenWeb("cabinet");

            SPSite oSite = null;
            SPWeb oWeb = null;


                try
                {
                    SPSecurity.RunWithElevatedPrivileges(delegate()
                    {
                        using (oSite = new SPSite(site.ID))
                        {
                            using (oWeb = oSite.OpenWeb(web.ID))
                            {
                                oWeb.AllowUnsafeUpdates = true;

                                SPQuery query = new SPQuery();
                                query.Query = String.Concat(
                                    "<Where>",
                                                "<Eq>",
                                                "<FieldRef Name=\\"ItemNumber\\" />",
                                                "<Value Type=\\"Number\\">" + Id + "</Value>",
                                                "</Eq>",
                                    "</Where>");
                                query.ViewFields = String.Concat("<FieldRef Name=\\"ItemNumber\\" />");
                                query.RowLimit = 1;
                                SPListItemCollection listItems = oWeb.Lists\["ListName"\].GetItems(query);
                                // perform if item returned
                                foreach (SPListItem Item in listItems)
                                {
                                    try
                                    {
                                    String FilePath = String.Format("{0}{1}", Server.MapPath("~/\_doc\_