Chinese Teacher John, the main thing is "What are you trying to say?" The key meaning of these two sentences is "Not today" or "Not this time." So you are basically saying No. Socially these are not treated as a promise or an invitation. Is this the effect that you intend?

"What's the difference?"

In that situation, they have the same meaning, although "some" carries a very non-specific tone in most cases. Another means "one other" and is typically used when the "other" is something known. Some other means "any other" and is used when the "other" is not necessarily known.

What do you mean to say? In what kind of situation?