Hi Adam Patacchiola,
OpenAccess does not allow having mapped classes in web applications (including web services). You can create a separate Class Library project and have the reverse mapped classes in that project. Then you can reference it from the web service and use the persistent classes. Additionally, you should "Enable" the web service after you have set the project reference to the class library. That will create the necessary "openaccess" node in the configuration file and add there a reference to the class library assembly.
the Telerik team