JAVA - Form Loaded With Errors - How can I import and open a project that uses JCalendar.1.4? (NetBeans)

Question

I get the following error message when I try to use a form in this project. The project uses the library JCalendar.1.4. I already downloaded the library and I did this to add it I clicked on:

• Tools
• Palette - Swing/AWT Components
• I created a New Category called "JCalendar"
• Add from JAR. Then I selected the folder where I have the library and I chose all the components to add them to my palette. I did not work. I'm a very beginner so this is the first time I try to do this.