What is Wrong with this Sentence?

[4rumid]

I'm not sure I agree, Celeste.

A cost efficient way to have multiple articles online that contain links back to your site is to utilize one of the many websites that post articles for free."

I don't see a problem with subject/verb agreement at all.

The subject of the sentence is "A cost efficient way" (singular); the verb is "is" (singular).

If the question is with "one of the many websites that post articles for free" I don't see a problem there either. "one" doesn't have to agree with anything. You're talking about "many websites that post" not "one website that posts."

[Celeste Stewart]

I don't really know what the editor specifically found wrong, but there are four verbs in this sentence and the only one that looked like it could be interpreted with an agreement issue involves the "one of many that post(s)." The OP originally asked us what was wrong with the sentence and we came up with some pretty good revisions, even without focusing on the subject/verb issue. In my opinion, the original sentence is awkward and could benefit by being simplified which would probably solve any subject/verb agreement issues.

[4rumid]

Yup, I agree completely.