Try the following:
1- Close Visual Studio
2- Uninstall LLBLGen Pro v.2.0
3- Install LLBLGen Pro v.2.5
4- Open your application in Visual Studio
5- Make sure you reference the newly generated code of v.2.5
6- Make sure your application references the v.2.5 runtime libraries.
7- Make sure the new EntityCollection appears in the toolbox.
8- Re-Build the application.