You’re correct in that the first example is wrong, and that it’s hard to nail down exactly why. The two phrases are quite similar, and in your second case neither is correct. If you swap “except for” to “also” why would you usually just use “other

than”?

”

is clearly wrong.

Why do the two phrases have overlapping uses, but are not equivalent.

Could you rearrange your answer slightly to avoid ambiguity?

If “without success” is not intended to be so, what is the context against “unsuccessfully”?

Personally, I fail to see how one can read either of your sentences (or my modified example) to mean that you have “tried to fail” since the adverb “unsuccessful” (or the adverbial clause “without success”) clearly pertains to the verb “to try”.

What are your first two sentences? Can you fix them?