DNN - Enable custom CSS classes to appear in Telerik Editor

Hi there, I have a DotNetNuke 6.1.4 installation and wish to add some custom CSS classes in the CSS dropdownlist in the Telerik RadEditor. I have added the [login to view URL] file and it seems to be detected however the classes in the 'Apply CSS Class' remains empty. I have followed all known instructions to no avail, so I am looking for someone with extensive experience with DotNetNuke to diagnose and get the CSS styles appearing. Look forward to hearing from you.