My formula:
=IF(ISERROR(MATCH(K494,WWP_Installs!C$2:C$490,0)), "Unk",WWP_Installs!K$2:K$490)

K494 = 1980A 18th AVE NE
WWP_Installs!C$2:C$490 = 1980A 18th AVE NE
WWP_Installs!K$2:K$490 = 256M/64K

But result of formula is #VALUE

when performing calculationsteps, it say the cell (K494) contains a constant.