Mendix URL only available after pressing F5

Today I went live with a Mendix application for a customer, and I'm getting back the following feedback: "Everytime I go to the application URL the log-in page gives the following error: Error when loading url Login/loginform.mxf. Could not load class loginsystem.widget.LoginForm" After pressing F5 to reload the page the error is gone and the login page loads correctly. They are mainly using IE8 as browser. What could be causing this behaviour, and more important, what could solve it?
1 answers

Could it be something with caching or a proxy used by your customer?