It looks like you are using string manipulation to convert your CoverageEffectiveDateKey and CoverageEndDateKey from yyyymmdd format to mm/dd/yyyy format. DATEDIFF is perfectly capable of handling strings in yyyymmdd format, so don't bother doing the string manipulation. (You may still need to convert to a string if your fields are INT keys.)
Drew
J. Drew Allen
Business Intelligence Analyst
Philadelphia, PA