iPad UIWebView and different versions of XCode

Question

I have an iPad app with a UIWebView which loads some local .rtfd.zip files. The problem is that if I compile the app with XCode 3.2.2, everything works fine, but if I compile it with newer versions of XCode, I just get a blank UIWebView. Here's how I load the files into the UIWebVIew:

-(void)loadFile:(NSString*)file
{
NSString* resourcePath = [NSBundle mainBundle] bundlePath;
NSString* sourceFilePath = resourcePath stringByAppendingPathComponent:file;
NSURL* url = NSURL fileURLWithPath:sourceFilePath isDirectory:NO;
NSURLRequest* request = NSURLRequest requestWithURL:url;
webview loadRequest:request;
resourcePath release;
}

All the testing is done in the simulator. Can you help me? Thanks in advance!