Delphi is unable to locate the form's class declaration in the interface section of the unit. This is probably because the type declaration containing the class has been deleted, commented out, or incorrectly modified. This error will occur if Delphi cannot locate a class declaration equivalent to the following:

type
       ...
       TForm1 = class(TForm)
       ...

Use UNDO to reverse your edits, or correct the declaration manually.