Since we had a refresh bug in the calendar widget I decided to update the calendar widget with the latest version but with the result of the famous no constructor found error on every page where this widget is used. It seems I am not alone (see this forum post https://community.mendix.com/questions/9104/Calendar-Widget-Update. I hope somebody from Mendix can chime in here why these no constructor found errors are happening, because in my opinion they happen to often and emptying the cache is not always (but most of the time is) the sollution. When debugging with chome I notice the following: There are two warnings The XMLHttpRequest progress event property 'position' is deprecated and will be removed in M50, around April 2016. Please use 'loaded' instead. See https://www.chromestatus.com/features/5044837464145920 for more details. Synchronous XMLHttpRequest on the main thread is deprecated because of its detrimental effects to the end user's experience. For more help, check https://xhr.spec.whatwg.org/. Then you have the error mxui.js?635960764363557534:29 No constructor found for widget calendar.widget.calendar Line 29 is however 934964 characters so I will not post that here. Since cacheburst is also mentioned I placed my index.html below. If other information is needed let me know. Regards, Ronald [EDIT] The problem is in the Javascript of the widget. Nick van Wieren had the sollution. I have requested a pull request on github so hopefully the widget gets updated soon in the appstore. <!doctype html> <html> <head> <meta charset="utf-8"> <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1"> <title>DaywizeCloud</title> <meta name="viewport" content="width=device-width, user-scalable=no, initial-scale=1, maximum-scale=1"> <meta name="apple-mobile-web-app-capable" content="yes"> <link href='https://fonts.googleapis.com/css?family=Open+Sans:400,600,700,300' rel='stylesheet' type='text/css'> <link rel="stylesheet" href="lib/bootstrap/css/bootstrap.min.css?{{cachebust}}"> <link rel="stylesheet" href="styles/font-awesome.min.css?{{cachebust}}"> <link rel="stylesheet" href="mxclientsystem/mxui/ui/mxui.css?{{cachebust}}"> <!-- Want to use SCSS? Place the line below between comments --> <link rel="stylesheet" href="styles/lib/lib.css?{{cachebust}}"> <link rel="stylesheet" href="styles/custom.css?{{cachebust}}"> <link rel="stylesheet" href="styles/custom-bootstrap.css?{{cachebust}}"> <link rel="stylesheet" href="styles/font-awesome.min.css?{{cachebust}}"> <!-- ICONS EXAMPLE --> <!-- iPhone retina icon (iOS < 7) --> <!-- <link href="resources/ios/icons/apple-touch-icon-precomposed-114x114.png" sizes="114x114" rel="apple-touch-icon-precomposed"> --> <!-- STARTUP IMAGES --> <!-- <link href="resources/ios/startup/apple-touch-startup-image-1496x2048.png" media="(device-width: 768px) and (device-height: 1024px) and (-webkit-device-pixel-ratio: 2) and (orientation: landscape)" rel="apple-touch-startup-image"> --> </head> <body dir="ltr"> <div id="content"></div> <script> dojoConfig = { baseUrl: "mxclientsystem/dojo/", cacheBust: "{{cachebust}}", rtlRedirect: "index-rtl.html" }; </script> <script> if (!document.cookie || !document.cookie.match(/(^|;)originURI=/gi)) document.cookie = "originURI=/login.html"; </script> <script src="mxclientsystem/mxui/mxui.js?{{cachebust}}"></script> </body> </html>