Duplicate Content Problem!~

One of the sites, that I optimize is a very peculiar case. I had already been done everything in my power to pull it into the lead in the search results. To no avail. However, the strangest thing is that the other site, was about the same subject and I have been optimizing it on the same phrases after when, the other site very quickly reached the 1st place. I had been wondering what could be the cause of this situation, so I typed in the browser, a piece of text from the page, which allegedly was written personally by my clients ..

Oh stupid Me..! How could I not think of before, that the text on the page is not unique! Although we always ask our clients to care about the original texts on the websites and if they have no ideas about it, we offer them to write unique text. But I didn't even think, that the entire text on her - my client's page (who assured us that interceded content is original created by her) will be alive and completely copied from other texts found in the network!

So I have written new texts to the site and I ping them. After, about 2 weeks, the site finally have started to move from the place. But still, site did it sluggishly and reluctantly, and finally, at one phrase, site stuck in 16th place. Her site still can;t break into the magical top ten.

And I still have no idea what the problem is in. Is it possible that using the same method of positioning the two sites, put one site (easily) in the lead, and the other may not be able to break even for the top twenty? Or maybe it's just punishment for keeping on website kilo plagiarism for so long? -, -