Scanning issue on our HP 9050 MFP

This is a very common problem. Most people notice the large "platen" glass where you lay down a copy to manually scan it. But if you look you will see there is another thin glass above it. This is where the unit scans when you use the auto document feeder. Basically the scanner does not move, only the paper does.

So when the paper is moving over that thin glass window, a "DOT" on the glass becomes a "LINE" on your copy.  

So what you need to do is look very closely at that thin little window and you will probably find some white-out or other obstruction which is blocking the scanner from seeing the page. A lot of times you can miss it becuase its usually small enough where you have to look close to see it.

Remember, scanners can see about 1,000 times better than the human eye, so it doesn't miss anything. And the fact that you said "purple" it also leads me to believe it is White-Out which is a common color it produces when it is the obstruction blocking the scanner's ability to see the page.

But remember, anytime you can PRINT and SCAN from the MAIN PLATEN with no problems but from the document feeder you get a bad result, immediately look to the smaller thin platen glass for an obstruction.  

Now, if you get a line from both printing and scanning, then this is in the imaging unit itself. That would be your drum, image transfer unit or if it has a charging wire, then a dirty charging wire. Those are the basics.  

Hope this helps.