Ok, I just started with a brand new workspace, and I have the same problem. After a little more investigation, I see that my Web-root folder under the Web section of the MyEclipse preferences is wrong. It’s set to ‘Webroot’, and it should be ‘Web Content’. Where does this get set? Why can’t I change it?
I had the undefined archive location message when trying to explode my web application. There were two problems: I hadn’t informed well two fields.
1) Window -> Preferences -> MyEclipse -> J2EE Project -> Web Project -> Web root folder name: [I put web which is the name of my super WEB-INF folder]
2) Package Explorer -> [right click project] -> MyEclipse -> Web -> Web Context root: [I put the name of my application: WHATEVER] (will be the name of the folder under the tomcat’s webapps folder where the application will be exploded).