Description
You see this error message when the tiling schema file is corrupted or not accessible. The tiling schema file is usually named conf.xml and is found under the cache folder.
Solution
Make sure the cache directory is accessible and the tiling schema file (conf.xml) is valid. You can examine the tiling schema file by opening it in an XML editor or in Notepad and making sure the XML syntax is valid and all necessary sections are present in the tiling schema file.