Our main website is all original content. However, in June we worked with an author to adapt an existing article from his website for our readership. Eg: if his article was about widgets, the adapted article was about 'using widgets in a blue context'.
The pages were published in July, but today have a pagerank of zero (the only ones on our site that are zero). Ranking and visitors have declined since the first few weeks after publication.
I guess it is possible the PR hasn't been updated yet, but we think it is more probably a penalty due to duplication because, despite having a completely different emphasis, many sections of text are identical to the original articles.
For future articles I guess the lesson is not to adapt, and to instruct authors not to re-use any text.
In the short term, however, we have to decide what to do with these pages. Our options are, I think, to leave, delete or re-write them (using same or different page URLs).
I would like (with the original author's involvement/permission) to rewrite them, using the same page URLs. However, I'd appreciate whether the experience in this group is able to foresee any problems with this that we haven't anticipated.