Forget the bar exam for lawyers or the SATs for high school seniors. A mandatory nationwide licensing test for reverse-mortgage counselors is stumping veteran housing specialists, some of whom have been advising elderly homeowners in the Charleston [South Carolina] area about this type of loan for years. Several months after the federal government made the exam more difficult, no Lowcountry housing counselor has been able to pass the exam. As a result, area homeowners in search of the required counseling are being referred to agencies in Columbia or Greenville.