Issue
When you try to move content or widgets across stages, the action fails and you see the following error message:
Probable Causes
The content that you are trying to move is part of an existing widget.
Unstable network or internet connectivity issues prevent movement of content or widgets across stages.
Suggested Solutions
Consider a Flow (content) attached to a Pop-up (widget) in the Production Stage. When attempting to move the Flow back to the Draft Stage, a message appears indicating that the Flow is associated with a Pop-up in the Production Stage. Clicking Send to draft moves the Pop-up to the Draft Stage along with the Flow.

Similarly, if a Task List (widget) contains content attached to it in the Production Stage, a message appears indicating that some content is associated with the Task List. Clicking Send to production moves all content along with the Task List to the Production Stage.

Check your internet connection and try again.
For more information, see Can I move Contents/Widgets that are attached to another Content/Widget across stages?
Note:
If the issue persists, contact suport@whatfix.com.