When using SUM() it reports 0, instead of 150.

The 3 cells I'm calculating are VLOOKUPs which equal 50, 50, 50. I
then use SUM(C27:C29) to report the total. This however reports 0.
If I override the VLOOKUP formula by entering 50 in each cell, I then
get the correct value using SUM.


Why is this happening? I'm using the exact formula elsewhere in the
spreadsheet and it works fine. I'm at a bit of a loss.


Thank you.


These are the exact formulas used:
=IF(C2="", "", VLOOKUP(C$2, ProCentre!$I$9:$K$30, 2, FALSE))
=IF(C2="", "", SUM(C27:C29))