Someone told me that my last blog post didn't make any sense, so I will try again.
If, as part of tying off your warp chain you tie the four 'arms' of the cross (X), untie them before you begin spreading the warp chain to the width required in the reed.
In this photo you can see how I've tied in four places, one on each side of the lease sticks on the 'top', one each side of the lease sticks on the 'bottom'. (If you can't see the entire photo, try right clicking on it and open in a new tab to get the full version. Blogger seems to be cropping photos in ways that don't show the entire picture.)
If these ties are not removed, they will prevent the threads from spreading out to the width needed in the reed.
Hope this makes more sense.