"BindingSource cannot be its own data source" - error when trying to reset the binding source from a method in another class

The problem is that you can't update a BindingSource within a thread other than the gui thread. This is due the fact, that the BindingSource will fire some events which will then be received by your data grid view which will then start to update itself, which will fail cause it won't be done on the gui thread.

So right before you call RunWorkerAsync() you should call class1BindingSource.SuspendBinding() and within your RunWorkerCompleted you should call class1BindingSource.ResumeBinding().

Also ensure that within your DoWork you won't call any methods on the binding source (like you did with bs.ResetItem(0)).

And also remove this lock statement. It simply doesn't make any sense (in your example) and if you really need it (in your real code) consider using some private object _Gate = new Object(); within your class to avoid any deadlocks from the outer world, cause bs.SyncRoot is publicly available.

I had the same problem: - BindingSource that had elements with INotifyPropertyChanged - A separate Task that updated the elements.

The suggested solutions SuspendBinding etc didn't work. BindingSource should have done something like IsInvokeRequired.

Luckily Ivan Stoev came with the brilliant idea of subclassing the BindingSource and do something similar as IsInvokeRequired. Thank you Ivan!

Link: Update BindingSource from a different Task