The message you're seeing is what happens when you're using a copy of the file for the amended, not the original file that you used to file the original return....I know you said you "followed the instructions" but I have no clue what those instructions actually say.

If you had a file that you originally Efiled named   JonesTom.19i you have to use that same file (with the same file name) for the amended return.  If you made a copy and called it JonesTomAmended.19i and are trying to use that to Efile an amended return, it wont work.