Well the first part is when you have your web.xml includes the tag libraries, and the classpath is set, then a restart of IntelliJ IDEA is needed.
The second part is the dtd that the xml file is pointing to. It appears that some tag names added hyphens in them, whereas an older version did not have the hyphens. Try typing "<" and see the drop down that occurs and the tags that are available. This is also a way to make sure that your classpath and tag libraries are correct.
Good Luck and I hope that helps. At least that worked for a co-worker's machine when he was having the same problem.