If you are trying to download form one admission letter and it is not available then make sure that you are using the correct KNEC code, you are selecting the correct county and sub-county where the student did his/her KCPE exams, and you are using the correct link (i.e. For National Schools or Extra County Schools or County Schools or Sub-county schools).
If you have confirmed that you have met all the conditions above and the admission letter is still not available for download then contact the ministry of education placement office through email at placement@education.go.ke or visit your county director of education for support.