You are attempting to delete the entire Keywords table because of this.
DELETE dbo.Keywords
WHERE @nKeyWord_IdArg = @nKeyWord_IdArg
You have the same variable on both side of the predicate. Pretty sure that all you need to do is remove the @ from one of them. 😉
There are definitely some performance improvements you could make in here if you are interested.
--EDIT--
Looks like John beat me to it. 😀
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