we tried the code that you provided in order to reproduce the error but we failed. Everything worked as expected for us.
What we did was:
1. We created the same exact classes that you provided.
2. We entered some information.
3. We used Linq/Sql/Oql to retrieve a record and pass it to your method.
Everything did worked for us.
The exception itself usually indicates one of the following:
1. The persistent object was removed from the database.
2. The object ID used to retrieve the persistent object is not
a referring to a persistent object.
Most likely, you are attempting to access an object that has been
deleted or has not been stored.
If you are still unable to find a resolution for this problem please notify us, we will elevate the forum thread to a support thread, therefore you will be able to attach a small project that represents the problem and we will investigate it further.
the Telerik team