This error occurs when there is at least 1 Question ID in a calculation that does not exist in the Project. This error message may also be accompanied by specific Question IDs, which will be helpful in narrowing down the root cause of the error. This can happen when copying a Form from another Project and may not have been properly checked to accommodate the Question IDs that are available in the current Project.
In order to find the cause of the error, it is recommended to open the affected Form in Workflow > Edit Forms and check all questions by clicking Edit Question and checking the values shown in the calculation box (if applicable).
You can cross-reference Question IDs in your calculation against available Question IDs by clicking on the link "Click here to view the IDs for this Form".