Cell-dependent drop-down

Morning all,
Should be a quickie;
What's the best way for me to do the following...

Say in A1 i have either Yes or No, in B1 i have a dropdown validation from a list if A1 is Yes and "n/a" if A1 is no.
I thought if i renamed my list validation to "Yes" and labelled "n/a" as "No", then using =INDIRECT(A1) as my list validation would do the trick.
Alas no.

Where am i going wrong?

Cheers,
TRC