Hi Alex,
One of our partners recently ran into this issue. Here is what resolved it.
Matt: If that doesn't work, check the names of your sections. I just had this happen and it turns out that one of my sections got renamed when copying the screen and one of the screen load actions called another action that shows or hides that section and that is what was causing the error for me. Hope that helps.
If this isn’t the issue you can try clearing your browser’s cookies and cached files or try using a different browser. You can also take a look at this thread, as your issue may be related.
Please post back here and let me know if you were able to resolve this or are still having this issue.
-Audisho