IF Statement returns either Value error or False

[katja328]

if Statement A: =IF(M4>$B$17,0,LOOKUP(M4,$AA$20:$AB$29)*$B$15/12) works very well

if Statement B: =IF(M4>$B$17,0,LOOKUP(M4,$AA$36:$AB$44)*$B$15/12) works well too

now I am trying to say

=IF('Input Page'!B36="yes",(IF(M4>$B$17,0,LOOKUP(M4,$AA$36:$AB$44)*$B$15/12),(IF(M4>$B$17,0,LOOKUP(M4,$AA$20:$AB$29)*$B$15/12))))

Basically, if B36 is yes, use If Statement B, otherwise IF Statement A. If I write Yes, I get a "Value" error, if I change the yes to 1, I get a FALSE error.

What am I doing wrong?
Thanks

[NBVC]

Maybe should be?

=IF(M4>$B$17,0,IF('Input Page'!B36="yes",LOOKUP(M4,$AA$36:$AB$44)*$B$15/12,LOOKUP(M4,$AA$20:$AB$29)*$B$15/12))

[NBVC]

or simplified:

=IF(M4>$B$17,0,$B$15/12*LOOKUP(M4,IF('Input Page'!B36="yes",$AA$36:$AB$44,$AA$20:$AB$29)))