Thank you for writing.
The reason why the exception is thrown and not internally handled is because we try to give as much flexibility to the developer as possible. This is why we have a validation mechanism where you can take care of the validation. You can read more about validation with RadPropertyGrid in our online documentation
Here is an example of how you can validate the case you have described using the PropertyValidating event:
sender, PropertyValidatingEventArgs e)
PropertyGridItem item = e.Item
TypeConverter converter = item.TypeConverter;
item.ErrorMessage = ex.Message;
item.ErrorMessage = String.Empty;
I hope this will be useful for you. If you have further question, I would be glad to help.
the Telerik team