I have a QT application. It has functioning QPushButtons that are connected to slots in my program. I am now trying to add a new button `myNewButton`, but somewhere, somehow it is not being registered.

For an existing, working button `myExistingButton` I have the line:

```
connect(ui->myExistingButton, SIGNAL(clicked()), this, SLOT(Foo()));

```

I cannot simply add the line:

```
connect(ui->myNewButton, SIGNAL(clicked()), this, SLOT(Foo()));

```

The compilation error is:

```
class UI::Viewer has no member named 'myNewButton'

```

And QT Creator does not list the button as an autocomplete option for `ui->` (i.e. I haven't simply mis-spelled the name). The records for `myExistingButton` and `myNewButton` are identical apart from coordinates and naming in the ui file. What could be causing this problem?