I am implementing a UITableView with UISearchDisplayController in xcode 4.2. UITableView & UISearchDisplayController are created in StoryBoard. I set the Cell Identifier
Use [self.tableView dequeue...], not [tableView dequeue...].
The cell you're trying to dequeue is linked to your primary view controller's tableView in the storyboard, NOT the searchDisplayController's newly created tableView (which has no cell identifiers linked to it). If you just message "tableView" then your dequeue message goes to the searchDisplayController's tableView since that's what was passed into the cellForRowAtIndexPath:... method.
-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
UITableViewCell *cell = [self.tableView dequeueReusableCellWithIdentifier:@"CellId"];
// do your thing
return cell;
}