I have had entries disqualified on several occasions, almost always through carelessness or oversight. I have also seen entries from the very best exhibitors disqualified. It is embarrassing, but less so for the novice, and it can be avoided. Here then is a summary of reasons for disqualification most often encountered by the novice. You have to write the correct name of the variety on the entry card and use the ARS show name.
Judges can even get picky about the spelling.
Take along your ARS Guidelines for Selecting Roses and check the name and its spelling even if you think you are sure. You have to write the correct class in which you are entering on the tag. This is not a big deal. Look at the show schedule. If in doubt ask the person doing placement.