Indirect Substtitute not working

DropList in C2 lists the Models in Col I (e.g. "Connect V408"), which have spaces in the names, so is named in the formula as "Connect_V408".

Cols J and K have derivates for each model (e.g. "GRAND TOURNEO") which have spaces in the names, so are named in the formula as "GRAND_TORNEO".

DropList in C4 SHOULD list the derivates for the choice in C2, using =INDIRECT(SUBSTITUTE(C2,"_"," ")), but isn't working.

Appreciate anyone who can set me right, as don't remember this problem before?

Ochimus