I've tried to illustrate my problem:

"NameID" is A1, "rs10170160" is B1, etc. Array data starts at A35

Name ID€¦..rs10170160
70001-1€¦..(formula here)

Formula: =vlookup(A2&B$1,A$35:E$38,4,False)

Array: (note, column C here is programmed in as =A35&B35)

70001-1€¦..rs10170160€¦..70001-1rs10170160€¦..C€¦..T
70001-11€¦..rs10170160€¦..70001-11rs10170160€¦..C€¦..T
70002-1€¦..rs10170160€¦..70002-1rs10170160€¦..C€¦..T
70002-13.....rs10170160.....70002-13rs10170160.....T.....T

Why does my formula keep returning NA when it should return a "C"??

Thanks in advance!