I am trying to dimension the position of several blocks in asketch using horizontal and vertical ordinates, but I get a messagebox stating "Cannot add a constraint on this entity."

I can still dimension to them using smart dimension and if Iexplode the blocks I can add the ordinate dimensions. I have triedsetting my ordinate zero at both the origin and on another sketchentity.

Edit: I am running SW2007 sp5.0SolidworksSketching