der Vollständigkeit halber habe ich noch folgenden Eintrag aus der KB ( Andreas wird den wohl kennen )
Date: 05.12.2001 ( und das ist noch Version 5 !)
Doc Number: 1093749
You create and save a form which can then be used as expected by end users. However, you then open the design of the form again to make a minor change and save the form. Once this is done, the form cannot be edited again. When you attempt to open the design of the form in Domino Designer, the following error displays and you cannot change the design of the form:
"Not a form."
Solution
This issue will occur through the improper use of subforms on a form.
The idea behind subforms is to be able to easily reuse the same code over and over again in different forms to alleviate duplicating your work. When using subforms on a form, you are able to insert each subform once. If you attempt to insert the same subform into a form more than once, an error message displays stating, "The subform already exists on the form." Domino Designer prevents the same subform from being placed on a form more than once because each of the fields on a form must have unique field names.
However, as a developer, your original subform may not contain any fields. It may just contain HTML code that you want to repeat in different areas of a form. To get around the inability to insert the subform in a form more than once, you insert your subform with the HTML code into two different subforms and then insert these two separate subforms in your form. Domino Designer initially allows you to insert the two different subforms onto the one form, but in essence, you have inserted the same subform on the form twice and have bypassed Domino Designer's error checking. This works the first time you save the form, however, the second attempt to edit the form will not allow you into the form and the error "Not a form" displays. Avoid using the procedure. You can use the initial subform once and if you need the code again, either create a second subform with the same code directly on the second subform or add the code directly on the main form.