Thank you for writing.
This exception is usually thrown when the source collection does not support add and delete operations. You should not experience this if you take the exact same steps as in the tutorial. The exception might be thrown if you are using custom query and/or your table adapters do not have an Update, Insert and Delete commands set (please check the attached screenshot). If you do not manage to solve this case, you can open a new ticket in our support ticketing system and send us a sample project which demonstrates your approach. This will let us get familiar with it, investigate what causes the exception and provide you with a more accurate response.
Do not hesitate to contact us whenever there is any development on this case or if you have any additional questions.
the Telerik team