Editing Form Fields in a SharePoint List

If you have been developing in SharePoint for any length of time, you have probably wanted to edit the default newform.aspx and editform.aspx to make it look a certain way of to hide columns in one view but not another. You can do this using SharePoint Designer by navigating to your SharePoint list and opening up NewForm.aspx. You may have deleted the exisitng ListFormWebPart, added your cuastom stuff, saved the form, and then tried to click on the new button in the list only to get an invalid URL dialog.

In order to prevent this DON'T delete the existing web part, hide it. Then add your custom list form and edit the controls and tables as you see fit.

Then you can save the form and click on the new button in the list and have it direct to your custom form.

The issue is documented in this Microsoft KB article.