http://technolog.nl/blogs/eprogrammer/archive/2007/07/24/HttpWebRequest-on-DotNet-2.0-driving-you-crazy-for-a-B2B-request_3F00_-Disable-ServicePointManager.Expect100Continue-first_2100_.aspxImagine, you have written a succesfull gateway to say, the European Community to check the validity of a VAT number. It always works, but suddenly it does not work anymore. What's up? Could it be that some service pack modified the behaviour of theenCommunityServer 2.1 (Build: 60809.935)http://technolog.nl/blogs/eprogrammer/archive/2007/07/24/HttpWebRequest-on-DotNet-2.0-driving-you-crazy-for-a-B2B-request_3F00_-Disable-ServicePointManager.Expect100Continue-first_2100_.aspx#1251Mon, 17 Dec 2007 16:16:55 GMT3420c8e2-8f96-4c4a-9e98-3bc38250dfb6:1251JohnThis is a tough one -- you can't know a priori whether the server can support Expect100Continue. The purpose of this property is to save bandwidth. The default value in the Framework is true, so you'll use it by default. If a request fails, set it to false and try again. John