Hi Mimi. Your second sentence means that, for some reason, you're afraid to not be able to come to my birthday party. For example, this means that you're afraid that if you don't come, I might be insulted. Or maybe you're afraid that if you don't come, I might never invite you again. Do you see the difference?Hi,
Can I say in two ways?
I’m afraid that I won’t be able to to come to your birthday party.
I’m afraid not to be able to come to your birthday party.