Running an iPhone app on the device only shows a white screen

I have a strange problem when I try to deploy my current app to the device.

Once it is successfully pushed down I see the Default.png as it loads, then the first view appears for about 1/10 second and the whole screen goes white. It feels like the it is a resolution issue or similar as I can still interact with the text fields. When I touch the text field the keyboard appears as normal and I can type in. I can also click-hold in the text field and the magnifying glass appears and shows everything underneath.

I have tried displaying a different view at launch to see if it was specific to the first view but to no avail.

I also tried a different device and it also happens there.

I am using iOS SDK 4.0.2 and the devices are 3.1.3 & 3.1.2

P.S. This all worked fine up to a few weeks ago, but I'm not sure what has changed to make this happen.

Thanks in advance Liam

Edit:

The app works perfectly in the simulator.

Snippet of the 开发者_运维问答code to display the view. It's a very simple page that is displayed if the person is not logged in. In the image the magnifying glass is in the 'username' field. This works fine in the simulator.

LoginPageViewController *loginViewController = [[LoginPageViewController alloc] initWithNibName:@"LoginPage" bundle:nil];
[self presentModalViewController:loginViewController animated:YES];

It turns out that the 'Main nib file base name' in the project's plist was loading a blank view on top of the view I was creating.

I still do not know why this only happened on the device and not on the simulator? perhaps a speed issue when loading?