See if your sound file follows these rules: IOS Docs: Scheduling, Registering, and Handling Notifications

Hope this helps.

Is this likely to be because it is taking too long to call it, or could it be something else?

Thanks in advance

An updated example from above would be:

UIApplication* app = [UIApplication sharedApplication];

// Create a new notification
UILocalNotification* alarm = [[[NSClassFromString(@"UILocalNotification") alloc] init] autorelease];
if (alarm)
{
     alarm.fireDate = nil;
     alarm.repeatInterval = 0;
     alarm.soundName = @"ExitSound2.wav";

     alarm.alertBody = nil; //Change this to nil and only the sound will play.

     alarm.hasAction=NO;

    [app presentLocalNotificationNow:alarm];  //This schedules the notification to happen ASAP
}