"This PNG contains additional data for Adobe Fireworks, which will be discarded upon save."

This prompt appeared when I had modified a number of files with Fireworks and then tried to execute a batch command in Photoshop on the files:

"This PNG contains additional data for Adobe Fireworks, which will be discarded upon save."

And although I clicked ok for the first file, it appeared again for each one--rendering the batch process useless. I couldn't find a solution in Google, so it seems that the only logical way to solve the problem was to run the batch using a Fireworks command instead. And it is just as easy to create a "command" in FW than an "action" in PS:

1. Open a file in Fireworks
2. Open the History dialog box
3. Make sure the History list is clear
4. Go through whatever steps you wantto modify the image as needed
5. In the History panel, highlight the steps that you want to set as the command
6. In the History options drop down select "Save as Command"
7. Give your command a descriptive name
8. Select File>Batch Process
9. Select the files you want to run the command against
10. In the next step (Batch Process dialog) open the Commands list and select the command you made.
11. Run it
12. Done!