This is a common error. You have to make sure there's just a dataview in your new and edit form. You can set the popup title in the properties bar of the new and edit buttons, therefore a title in the popup form will be unnecessary. If you open the new and edit forms in content, you can use a title in the form.
This is because you already give the popup form a title on the New or Edit button itself. Seeing as you can have only 1 title on a popup form, the modeler warns you to remove the title.
This does let you use custom titles based on which button is pressed instead of which form you open. So a button New could have the title New Employee and the Edit button has Edit Employee while both still using the same form/dataview.
The form you link the new and edit button to probably has a Title or something. Make sure there is just a dataview and nothing else in the form.
The title was indeed the problem. Any reason there can't be a title in there?