Question

I can't agree with you more

Answer 1

我非常赞同你的观点。

追问

I could not agree with you any more

追答

这个没怎么遇到过。
应该是一个意思，分开的 any more。
有个人回答的很详细，给你参考下。
Spoken English:

I couldn't agree (with you) more.

Use for emphasizing that you agree with something that someone has just said.

"more" 是比较级的 adverb 用来修饰 "agree" 这verb。
意思是：我不能同意得再多了。那就是：我非常同意。

Example:
A: This will satisfy everybody.
B: I couldn't agree more.

惯性地使用couldn't : simple past 时态. 因为所同意的事，是指A刚才说了的事。

I can't agree with you anymore.

这句中，"anymore"的理解最重要。
Anymore (adverb): means no longer, any longer再也不 的意思
Anymore 不是比较级adverb，没有再多的意思

是故通常这样用：

I don't live here anymore.
I will not agree with you anymore.从今再以后不再同意你的做法(以前常常认同)

因为anymore 的字意，故不会说
I can't agree with you anymore.(这是文法正确，但意义不明的英文句子。)
Just say: I can't agree with you./ I don't agree with you.

I can't agree with you ANY MORE.
注意：Any more 要分开。这样more才有比较级adverb的意思

Example:
He doesn't want any more = He doesn't want more.

Any 修饰 more，可以除去却不影响句意

同理：

I can't agree any more = I can't agree more.

Answer 2

我非常同意你的观点