Hello,
I have installed the dnn 4.4.1 source and i begun my  module developping whith this vesion using visual web developper,i have created the necessary database for that module(witch i called productCategory)
and i made the nacessary changes on info ,controller, dataprovider, sqldataprovider,......;
firsatable All things seem to be good but the problem is that when i click update the folowing error appears:
Error: ProductCategory is currently unavailable.
DotNetNuke.Services.Exceptions.ModuleLoadException: The type initializer for 'YourCompany.Modules.ProductCategory.DataProvider' threw an exception. ---> System.TypeInitializationException: The type initializer for 'YourCompany.Modules.ProductCategory.DataProvider' threw an exception. ---> System.MissingMethodException: Cannot create an abstract class. at System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean noCheck, Boolean& canBeCached, RuntimeMethodHandle& ctor, Boolean& bNeedSecurityCheck) at System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean fillCache) at System.RuntimeType.CreateInstanceImpl(Boolean publicOnly, Boolean skipVisibilityChecks, Boolean fillCache) at System.Activator.CreateInstance(Type type, Boolean nonPublic) at DotNetNuke.Framework.Reflection.CreateObject(String TypeName, String CacheKey, Boolean UseCache) at DotNetNuke.Framework.Reflection.CreateObject(String ObjectProviderType, String ObjectProviderName, String ObjectNamespace, String ObjectAssemblyName, Boolean UseCache) at DotNetNuke.Framework.Reflection.CreateObject(String ObjectProviderType, String ObjectNamespace, String ObjectAssemblyName) at YourCompany.Modules.ProductCategory.DataProvider.CreateProvider() at YourCompany.Modules.ProductCategory.DataProvider..cctor() --- End of inner exception stack trace --- at YourCompany.Modules.ProductCategory.ProductCategoryController.GetProductCategorys(Int32 CategoryId) at YourCompany.Modules.ProductCategory.ViewProductCategory.Page_Load(Object sender, EventArgs e) --- End of inner exception stack trace ---

Please help me.