"There is already an open datareader associated with this command which must be closed first"

Hello, Rich,

Your question has already been answered in the other thread (Ticket ID: 1462589) you have opened on the same topic. Please, see our answer there for more information.

However, I am posting the answer here as well in order the community to benefit from it. 

The following help article demonstrates different approaches for storing the changes from RadGridView to the database: https://docs.telerik.com/devtools/winforms/controls/gridview/populating-with-data/updating-the-database-with-ado.net

As to the specific error message, "There is already an open DataReader associated with this Command which must be closed first", it doesn't seem to be directly related to RadGridView. After some research in general programming forums, I have found the following threads that may be suitable for your case:
https://stackoverflow.com/questions/6062192/there-is-already-an-open-datareader-associated-with-this-command-which-must-be-c
https://stackoverflow.com/questions/18475195/error-there-is-a

We kindly ask you to use just one thread for a specific problem to contact us. Posting the same questions numerous times slows down our response time because we will need to review and address two or more tickets instead of one. Moreover, threads are handled according to license and time of posting, so if it is an urgent problem, we suggest you use a support ticket, which would be handled before a forum thread.

Thank you for your understanding.

Regards,
Dess | Tech Support Engineer, Sr.
Progress Telerik