Fix and also provide instructions to fix image upload issue in Drupal

I have a Drupal website. When attempting to upload an image to a page I get an error "The file could not be uploaded". I need this fixed on the site. I also require instructions on how to fix the same issue on other sites if this issue occurs again. When bidding for this project, please add "ABC" to prove that you have read these requirements. Once you make a bid, we will not renegotiate pricing.