sumanakuta?

I once again stumbled one a new expression.

Sumanakuta (proably spelled wrong).
It got translated to I'm sorry, same as in Sumimasen deshita.

Did I misinterpret it or is this some kind keigo-sumimasen or a slang-sumimasen?

Thanks

Maybe it was "sumanakatta," which is "-ta" (past) form of "sumanai," which is the informal speech for "sumimasen." So it is the casual speech for "sumimasen deshita," saying "I'm sorry (for something that happened

thanks AK!

Can you tell me when it is used? Like only with Family or friends or could it be used at other places as well?

thanks again

I'd say the only situation when I can imagine that being said is by a man to his woman/girlfriend. When/if says it, he really means it sincerely.

So I'd say it's "casual/familiar" speech that you should not use outside your own family (provided you are a guy).

Good coverage AK! You always beat me (not a race or anything)! =)

すまなかった comes from　済む meaning to "pass" or "allow" and in the case of "sumanakatta" and also "sumimasen", it means "not pass" or in actual use, "I'm sorry" or an even longer interpretation, "what I did, is not allowed"

Other forms include, "すまぬ" (sumanu), "すまん" (suman) but I often hear this spoken in poetry, music, samurai flicks or by old fashioned Japanese like Yakuzas, though people won't lynch you for using it in conversation (they might think its funny that you know it).
I use "すまん、すまん!" in joking with friends/classmates when I messed up on something (complete with my hand rubbing the back of my head -- I'm so turning Japanes-ah!LoL)