Assertion failure in UITableView configureCellForDisplay:forIndexPath:

you are never creating a cell, you just try to reuse a dequeued cell. but as you never created one, there is none.

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath;
{
    static NSString *cellIdentifier = @"cell";
    UITableViewCell * cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifier];
    if (!cell) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:cellIdentifier];
    }

    NSString *currentValue = [shareValues objectAtIndex:[indexPath row]];
    [[cell textLabel]setText:currentValue];
    return cell;
}

or try (only iOS 6+)

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath;
{
    static NSString *cellIdentifier = @"cell";
    UITableViewCell * cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifier forIndexPath:indexPath];

    NSString *currentValue = [shareValues objectAtIndex:[indexPath row]];
    [[cell textLabel]setText:currentValue];
    return cell;
}

from UITableView.h

- (id)dequeueReusableCellWithIdentifier:(NSString *)identifier;  // Used by the delegate to acquire an already allocated cell, in lieu of allocating a new one.
- (id)dequeueReusableCellWithIdentifier:(NSString *)identifier 
                           forIndexPath:(NSIndexPath *)indexPath NS_AVAILABLE_IOS(6_0); // newer dequeue method guarantees a cell is returned and resized properly, assuming identifier is registered

-dequeueReusableCellWithIdentifier: will always need a check, if a cell was returned, while
-dequeueReusableCellWithIdentifier:forIndexPath: can instantiate new one.