If WebEPG is configured to export to xmltv format and the resulting tvguide.xml is configured to be imported by XmlTv Importer, the import fails because there is no xmltv.dtd file (which is referenced in tvguide.xml produced by WebEPG).
We should provide a copy of xmltv.dtd in a default folder (%ProgramData%\MediaPortal\MediaPortal TV Server\xmltv) and set the folder as the default output of WebEPG and default input for XmlTv Importer