maximus12 - 4:45 pm on Jul 26, 2010 (gmt 0)
I had a similar situation. Back in June, a client of mine asked me to make a few modifications to his site. Please keep in mind that this site was untouched for 2 years and had all the same links pointing to a site my client marketed for. Navigational structure was also never touched. It had 1st page rankings for allot of good keywords for at leat 4 years.
He wanted me to changed 25 links to another url. The site he marketed for had a new product with a unique different URL and wanted him to oint links to their new URL.
I did this and 4 days later BAMMMM -50. So I am sure that this was the cause of the penalty. The site was not moved one inch for 2 years!
I am very sure that the problem was that I did not add no follow tags to the URLS. Which is a must nowadays
Adding no=follow is what I am about to do and then submit a recon request. But my experience has told me to wait at least 60 days before submitting a recon request.