I had this problem recently, and here is what I found. If you double click the CHKLST.AFD file, it will normally open in a text editor (Notepad or similar) and when you save your work, it will save the file with a .TXT suffix instead of the required .AFD suffix. If this happens, windows does not allow you to rename the file to correct the suffix easily. I went into the command prompt under the START button (lower left in windows) and from there type "E:" or whatever the drive letter is with your SD card. Then type "rename chklst.txt chklst.afd" and that will get you on your way.