Can an employee have more than one record? If not, this seems to work:
strFilter = "(Nz([7],0)+Nz([8],0)+Nz([9],0)+Nz([10],0)+Nz([11],0)+Nz([12],0))-24 > 0"
stDocName = "2011 Sick AbuserTbl MM Report"
DoCmd.OpenReport stDocName, acPreview, , strFilter
You can't have the Sum() function in the wherecondition, so this looks at each individual record. In my brief tests, this triggers the no data event, and as expected the second message from the error handler.