On Sep 9, 2013, at 5:34 PM, Peter Strauss <ko6r@yahoo.com> wrote:

I have successfully downloaded, modified and uploaded memory settings.
I thought that I could save such a file, and then use it for a subsequent upload if that became necessary.
What I did: I used what I had saved from a previous download, modified it, and then attempted to upload it. I got an error:
Failed to communicate with radio: Radio did not ack block 0

Can I only upload the same file that I downloaded? If that's the case, why would one save a file?

You should be able to do exactly what you are suggesting, at least when using the same radio. That you couldn't means something went wrong. To help, people will need to know what version of CHIRP you're using, and what radio you are using. What operating system and programming cable you're using might help too.