what are you trying to do - load software or write a floppy. Are you using audio or serial connection
if you are writing a floppy you could have bad floppy, floppy heads need to be cleaned or floppy drive needs to be calibrated etc etc
a few things i learnt using adt pro loading software into an apple ii using the audio method
1 : allot of the software out there does not work. Was trying to load the game elite on an apple ii. just would not work. checked leads, connections, volumes. It finally worked when i tried a fourth image from the net. so the first 3 images i downloaded were all faulty
2 when loading software into the apple from a laptop or desktop , disable all system sounds. I found that even moving the mouse, on the machine that was 'playing' the image was enough to upset the process.
After the above mentioned I found adt pro to be great and it worked every time (unless a bad disk image)