URLForResource returns nil

I had a similar problem. The answer for me was to check the Target Membership of object's identity.

After some considerable digging and a smidgeon of luck I found that

    NSURL *fileUrl = [[NSBundle mainBundle] URLForResource:@"embedded" withExtension:@"html"];

is incorrect and I should be using

    NSURL *fileUrl = [[NSBundle bundleForClass:[self class]] URLForResource:@"embedded" withExtension:@"html"];

instead.

i.e. NSBundle bundleForClass:[self class] and not NSBundle mainBundle will give access to a screensaver bundle.

Might be obvious, but only if you know ;)

See Apple Developer NSBundle Class Reference