In some cases, particular on shared hosting, parts of the page rendered using AJAX display wrongly or not at all. Typical areas where this is most noticeable include the back end category treeview control, and front and back end areas that are within a tabbed dialog.
The first thing to check is that your site is set to run the correct ASP.NET version. For Kartris v1.4, this is ASP.NET 4.0. For earlier versions of Kartris, set it at the server to use ASP.NET 2.0.
The cause can be a lack of ASP.NET AJAX support on the server. But in some cases where this is present, it simply requires the handler mappings (in IIS7 or above) to be reverted. It is not immediately clear why this should be the case, but several customers have reported that this has fixed the issue.