I Discovered Error 5100 Fix ! (1) Open Cartridge door, Wait for Cartridge Cradle to Park, Unplug Printer. (2) With a Flashlight look in the Doors Center where Cartridge Cradle Belt is. Belt is Horizontal going from Left to Right. You will see a 1/8 Inch Wide Clear Plastic Ribbon that's Horizontal going from Left to Right by Center of Cradle Belt. This Clear Plastic Ribbon has Tiny Vertical Gold Lines Printed on it that can be seen with a Flashlight. These Tiny Vertical Gold Lines in Clear Plastic Ribbon tell the Printer Program the Position of Cartridge Heads. (3) Inspect the Clear Plastic Ribbon for any Grease and Dirt that probably got transferred Transferred from Cradle Slide. Whenever this Cartridge Door is Open people sticking there fingers inside can Accidentally Transfer Grease onto the Clear Plastic Ribbon by touching the Greased Cradle Slide on the Button that is Horizontal going from Left to Right. (4) When Grease and Dirt gets on the Clear Plastic Ribbon the Program Can Not Tell where the Printer Heads are. At Location where Grease and Dirt is the Printer Head will not Print any Ink and a Blank Spot will appear on Print. The Blank Spot will appear in the same place throughout the Printed Page from Top to Bottom. After Printing and Heads Park the ERROR 5100 will appear on Screen. The Program will sense the Head Position Read Error because Requested Dots to be Printed don't Print at Location of Grease or Dirt on Ribbon. (5) The Fix Is; Simply Clean the Clear Plastic Ribbon with Alcohol and Q-tips until Ribbon is Completely Clean ! Power Unit On and Print Test Page. I read these Forums. Everyone thinks Error 5100 is Damaged Print Head. Yes that's the Definition. I tried all Forum stuff. Nothing there worked. I discovered Grease on Clear Plastic Ribbon. Cleaned it. 5100 Error Is Gone !