Do you have a copy of the .tax2014 data file for the original return, before the first amended return? The easiest way to prepare the second amended return would be the following. Make a new copy of the original .tax2014 file with a different name (so that you don't damage the original file). Open the copy and, without going through the amend process, make the changes that were made by your first amended return. You now have a dummy "original" return that incorporates the changes from the first amended return. This dummy return is the base for the second amended return. Now start the amend process and prepare the second amended return.
If you don't have a copy of the .tax2014 data file for the original return, and you are amending only the federal return, not the state, you should be able to delete Form 1040X, which will leave you with a 1040 "original" return that includes the changes from the first amended return. Then start the amend process over again and it will make the adjustments against the numbers from the first amended return. Do this on a new copy of the .tax2014 data file with a different name so that you retain a copy of the first 1040X and you don't take a chance of messing up the original file.
