How To Write A Letter For Unable To Perform Something . Explain, if possible, why you are unable to fill the order or give the requested information. Remember that most of the mistakes are unintentional, so give a space to the other party to rectify the problem or settle the issue. 27+ Cover Letter For Bank Teller Cover letter for resume, Cover from www.pinterest.com Remember that most of the mistakes are unintentional, so give a space to the other party to rectify the problem or settle the issue. You can simply tell the employee about the problem of not performing duties and warn him in the letter. If you were working on a project, you could offer extra hours to work on the project.