I can verify that I’m using both (latest versions) together successfully. There may be a third plugin or a theme issue causing the conflict. I would recommend the following steps:
Disable all of your plugins except Gravity & ACF. Switch over to the default theme. Can you create a new form now?
If so, switch to your custom theme and try again. Then, enable your plugins one by one until you find the culprit.
Hope that helps!
Dalton
