looks like a few typos creeping in there......, NBVC's should be

=IF(ISNUMBER(MATCH(AA2,'Student List'!AE$2:AE$673,0)),INDEX('Student List'!B$2:B$673,MATCH(AA2,'Student List'!AE$2:AE$673,0)),"")

and Donkeyote's....in Excel 2007 only

=IFERROR(INDEX('Student List'!B$2:B$673,MATCH(AA2,'Student List'!AE$2:AE$673,0)),"")