A group of Microsoft Products and technologies used for sharing and managing content, knowledge, and applications.
Hi Rochelle,
If this issue occurs on a classic site, you may refer to the following steps to fix the error on SharePoint Designer 2013:
- Open the site in SharePoint Designer 2013;
- In the left navigation panel, click Lists and Libraries;
- In the right side, click to open the problematic list;
- In the right side, click the New button in the Forms section;
- Enter the file name, then select "New item form", check Set as default form for the selected type;
- Also create a Edit form and a Display form by the above step;
- Remove all the other old forms by selecting them and click on the Delete button in the ribbon.
Please let us know if you have any further concerns.
Best Regards,
Nathan