AJAX TabContainer within FormView fails to insert\update data

Unfortunately that is true, you have to transfer the data manually as below:

Protected Sub SqlDataSource_Updating(sender As Object, e As System.Web.UI.WebControls.SqlDataSourceCommandEventArgs) Handles SqlDataSource_Patient.Updating

The following is how to reference a TextBox from a TabContainer inside a FormView:
Dim TabContainer_CaseInfo As TabContainer =                        CType(FormView_Main.FindControl("TabContainer_CaseInfo"), TabContainer)

Dim TabPanel_Basic As TabPanel =  
     CType(TabContainer_CaseInfo.FindControl("TabPanel_Basic"), TabPanel)

Dim DOBTextBox As TextBox = CType(TabPanel_Basic.FindControl("DOBTextBox"), TextBox)


More references:
http://stackoverflow.com/questions/969784/ajax-tabcontainer-inside-formview-not-inserting-values