That its a PDF suggests that the problem could still be related to the drivers, since my scenario was also only with PDFs. One way to test is to select the print as image option in Adobe reader. If the line disappears then the problem is with the driver.
Opening up the printer and cleaning out accumulated ink on the rollers and the bar that the ink cartridges slide along is also a good idea, but I don't know if that will help here.
Thanks for your help.
Like I said it is a PDF file, I just discovered that the file was converted to Word 97, I decided to give it a try and save it as Word 2010 (added the name "copy" to prevent damage his original file) printed the page, Crossed my Fingers.... and it worked!
Apparently there was some minor incompatibility issue somewhere even though I still can't understand what caused this.
Thanks again for your help.