sumproducts producing #value errors

You don't use the -- on the summing range...

check range sizes (they should be the same)

check for value error in the ranges

check for text in the summing range...

=SUMPRODUCT(--(RawMarketers=$C$3),RawDateGap)/(SUMPRODUCT(--(RawMarketers=$C$3)))

If as it seems the data is stored in the same file as the calculation itself then there is no need for SUMPRODUCT at all

=SUMIF(RawMarketers,$C$3,RawDateGap)/COUNTIF(RawMarketers,$C$3)

which would be more efficient

or if using XL2007+ use AVERAGEIF