I just started lacing up a Miche 36h rear track hub (fixed/fixed, no dish) to a 36h Mavic Open Pro. Gene Spicer from Spicer Cycles and myself both independently calculated that the spokes should be 288mm long for 3x lacing (I used spocalc, he used shop software).
So I've been following Sheldon's guide, and installed all of the trailing spokes on each side without a hitch - when I was done, the hub was nicely centered in the wheel, and even the dish seemed right (yes, the spokes were still pretty loose - I still have about half of the threads showing). I could even hold the hub in my hand at this point and spin the wheel straight.
However - as soon as I tried to lace the first of the leading spokes, they don't seem to reach anywhere near where they should go! If I lace the spoke to cross three other (trailing) spokes on the same side of the flange, the leading spoke is short by a good 2 or 3cm. It's not b/c some of the nipples aren't seated in the rim all of the way.
It does seem as though it would fit in a 2x pattern, and that would be a disappointing mistake, b/c I want this to be 3x. But I don't think both of us made the same calculation error (I just checked again).
I've read and re-read the instructions a million times, and they make perfect sense to me - I just don't see why the hell this is happening.
Advice is very appreciated.
In this next image you can see that it is crossing three spokes, as Retro Grouch suggested: