JFrame Form being seen as java class...

OK, so i have this project to design a sport management program to run a school sport during a sports event. So I chose golf, coded the program, tested each window and everything works...

So then I run the whole project using all the options within it and using the highest possible values for all fields to test for errors and limitations, that works...

Immediately afterwards, I try opening a one of the windows in design view, which is a jframe form, in netbeans to edit its appearance, I get an error saying that there is an error loading the form or something. and that happens for all my windows in the program. I then clean & build it, during which I get a red text saying that a certain file in the build folder cannot be deleted. After the build, all the jframe forms (windows) in the program now appear as classes, ie I cant edit any in design view.

When I run them, they run normally, when I clean and build again, they still appear as classes and not jframes. I tried it out on several computers, all the same. One interesting thing is that when I add a new jframe form to the package, it compiles perfectly and appears as a normal jframe should, while all the original frames remaiin the same, as in appear as classes...

So now I cant edit appearances at all...

Is there anyway that I can fix this at all? Has anyone else had a similar problem?