let me provide some further details about what Nejc is suggesting as a possible solution...
Windows 7 (32- and 64-bit version) come with Internet Explorer version 8 included with the default installation (https://en.wikipedia.org/wiki/Internet_Explorer_versions
). Regardless of what you install and use later as your main browser, SketchUp relies specifically on the Internet Explorer.
In order for Modelur to run successfully, it needs Internet Explorer version 10 or newer and if you didn't update the default installation, the (too) old version 8 still lingers there, preventing Modelur for initializing properly.
What baffles most people in this respect is that sometimes Internet Explorer doesn't even appear on the list of installed programs at all or users at some point chose manually to uninstall it, selecting as default some other browser. Regardless of the situation, Microsoft decided that Internet Explorer should always stay installed on Windows and is in some cases just "hidden from the user's everyday view".
To sum up the proposed solution - you have to make sure you have Internet Explorer 10 or newer installed on your computer, either by (re)installing it or by updating it to the latest version.