Please change the RenderMode of the grid and let me know if it resolves the issue.Performing complex grid operations such as Inserting, Deleting, Updating, Hierarchy relations, Grouping, Exporting, Paging, Sorting, Filtering, etc. require accommodating appropriate database operations. Therefore, we suggest you to avoid Simple Databinding and strongly recommend the use of more advanced databinding methods, which automatically handle the aforementioned functions:
Declarative DataSource (DataSourceID property)
Programmatic Data Binding (NeedDataSource event, + DetailTableDataBind for hierarchy). You should set the DataSource property ONLY within these event handler.
Also, temporarily disable any AJAX on the page if present (RadAjaxManager, RadAjaxPanel, UpdatePanel, etc.) and enable your script debugger (FireBug or F12) to see whether there are any script or server errors interfering.