Please check the following points:

• Change to a recommended type of paper, and then check that the problem is solved. To see what is the recommended paper, click here.
  
  
• Check that the back cover is closed properly.
  
  
• Check that the transfer roller is installed properly.
  
  
• Check that the fusing unit is installed properly.
  
  
• Replace the fusing unit. To see how to replace the fusing unit, click here.