You might have a TV guide file (xml) with no stop times!
The default setting is to ignore programme tags with no stop times.
View the documentation of your grabber to see if including stop times is an option (a parameter?) or contact your XMLTV provider. You will get the best EPG quality if stop times are included in your file. If this is not possible, check "Calculate" in "Missing stop times" group when adding an XMLTV file.
If "missing stop times" is not the problem please click the “Validating xmltv files” link.