If you want to use the custom namespace of your WorkflowService which is in fact different than the default one “http://tempuri.org”, you have two ways to do that:

1. Brute Force method by using of XAML
2. Setting of namespace in property window.

Setting of Namespace in XAML

Setting of Namespace in property window

Read the complete post at http://developers.de/blogs/damir_dobric/archive/2010/01/20/workflow-services-how-to-setup-namespace-and-contract-name.aspx